net: poll/select low latency socket support
select/poll busy-poll support. Split sysctl value into two separate ones, one for read and one for poll. updated Documentation/sysctl/net.txt Add a new poll flag POLL_LL. When this flag is set, sock_poll will call sk_poll_ll if possible. sock_poll sets this flag in its return value to indicate to select/poll when a socket that can busy poll is found. When poll/select have nothing to report, call the low-level sock_poll again until we are out of time or we find something. Once the system call finds something, it stops setting POLL_LL, so it can return the result to the user ASAP. Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>hifive-unleashed-5.1
Eliezer Tamir
David S. Miller
parent
e4f2379db6
commit
2d48d67fa8
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@ -50,11 +50,25 @@ The maximum number of packets that kernel can handle on a NAPI interrupt,
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it's a Per-CPU variable.
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Default: 64
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low_latency_read
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----------------
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Low latency busy poll timeout for socket reads. (needs CONFIG_NET_LL_RX_POLL)
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Approximate time in us to spin waiting for packets on the device queue.
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This sets the default value of the SO_LL socket option.
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Can be set or overridden per socket by setting socket option SO_LL.
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Recommended value is 50. May increase power usage.
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Default: 0 (off)
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low_latency_poll
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----------------
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Low latency busy poll timeout. (needs CONFIG_NET_LL_RX_POLL)
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Low latency busy poll timeout for poll and select. (needs CONFIG_NET_LL_RX_POLL)
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Approximate time in us to spin waiting for packets on the device queue.
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Recommended value is 50. May increase power usage.
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Recommended value depends on the number of sockets you poll on.
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For several sockets 50, for several hundreds 100.
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For more than that you probably want to use epoll.
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Note that only sockets with SO_LL set will be busy polled, so you want to either
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selectively set SO_LL on those sockets or set sysctl.net.low_latency_read globally.
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May increase power usage.
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Default: 0 (off)
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rmem_default
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34
fs/select.c
34
fs/select.c
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@ -27,6 +27,7 @@
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#include <linux/rcupdate.h>
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#include <linux/hrtimer.h>
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#include <linux/sched/rt.h>
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#include <net/ll_poll.h>
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#include <asm/uaccess.h>
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@ -384,9 +385,10 @@ get_max:
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#define POLLEX_SET (POLLPRI)
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static inline void wait_key_set(poll_table *wait, unsigned long in,
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unsigned long out, unsigned long bit)
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unsigned long out, unsigned long bit,
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unsigned int ll_flag)
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{
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wait->_key = POLLEX_SET;
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wait->_key = POLLEX_SET | ll_flag;
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if (in & bit)
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wait->_key |= POLLIN_SET;
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if (out & bit)
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@ -400,6 +402,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
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poll_table *wait;
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int retval, i, timed_out = 0;
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unsigned long slack = 0;
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unsigned int ll_flag = POLL_LL;
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u64 ll_time = ll_end_time();
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rcu_read_lock();
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retval = max_select_fd(n, fds);
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@ -422,6 +426,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
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retval = 0;
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for (;;) {
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unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
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bool can_ll = false;
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inp = fds->in; outp = fds->out; exp = fds->ex;
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rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
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@ -449,7 +454,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
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f_op = f.file->f_op;
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mask = DEFAULT_POLLMASK;
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if (f_op && f_op->poll) {
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wait_key_set(wait, in, out, bit);
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wait_key_set(wait, in, out,
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bit, ll_flag);
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mask = (*f_op->poll)(f.file, wait);
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}
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fdput(f);
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@ -468,6 +474,11 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
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retval++;
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wait->_qproc = NULL;
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}
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if (mask & POLL_LL)
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can_ll = true;
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/* got something, stop busy polling */
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if (retval)
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ll_flag = 0;
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}
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}
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if (res_in)
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@ -486,6 +497,9 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
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break;
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}
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if (can_ll && can_poll_ll(ll_time))
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continue;
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/*
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* If this is the first loop and we have a timeout
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* given, then we convert to ktime_t and set the to
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@ -717,7 +731,8 @@ struct poll_list {
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* pwait poll_table will be used by the fd-provided poll handler for waiting,
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* if pwait->_qproc is non-NULL.
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*/
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static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
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static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait,
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bool *can_ll, unsigned int ll_flag)
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{
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unsigned int mask;
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int fd;
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@ -731,7 +746,10 @@ static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
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mask = DEFAULT_POLLMASK;
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if (f.file->f_op && f.file->f_op->poll) {
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pwait->_key = pollfd->events|POLLERR|POLLHUP;
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pwait->_key |= ll_flag;
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mask = f.file->f_op->poll(f.file, pwait);
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if (mask & POLL_LL)
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*can_ll = true;
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}
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/* Mask out unneeded events. */
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mask &= pollfd->events | POLLERR | POLLHUP;
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@ -750,6 +768,8 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
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ktime_t expire, *to = NULL;
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int timed_out = 0, count = 0;
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unsigned long slack = 0;
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unsigned int ll_flag = POLL_LL;
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u64 ll_time = ll_end_time();
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/* Optimise the no-wait case */
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if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
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@ -762,6 +782,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
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for (;;) {
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struct poll_list *walk;
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bool can_ll = false;
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for (walk = list; walk != NULL; walk = walk->next) {
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struct pollfd * pfd, * pfd_end;
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@ -776,9 +797,10 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
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* this. They'll get immediately deregistered
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* when we break out and return.
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*/
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if (do_pollfd(pfd, pt)) {
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if (do_pollfd(pfd, pt, &can_ll, ll_flag)) {
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count++;
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pt->_qproc = NULL;
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ll_flag = 0;
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}
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}
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}
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@ -795,6 +817,8 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
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if (count || timed_out)
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break;
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if (can_ll && can_poll_ll(ll_time))
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continue;
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/*
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* If this is the first loop and we have a timeout
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* given, then we convert to ktime_t and set the to
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@ -30,6 +30,7 @@
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#ifdef CONFIG_NET_LL_RX_POLL
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struct napi_struct;
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extern unsigned int sysctl_net_ll_read __read_mostly;
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extern unsigned int sysctl_net_ll_poll __read_mostly;
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/* return values from ndo_ll_poll */
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@ -38,17 +39,18 @@ extern unsigned int sysctl_net_ll_poll __read_mostly;
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/* we can use sched_clock() because we don't care much about precision
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* we only care that the average is bounded
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* we don't mind a ~2.5% imprecision so <<10 instead of *1000
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* sk->sk_ll_usec is a u_int so this can't overflow
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*/
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static inline u64 ll_end_time(struct sock *sk)
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static inline u64 ll_sk_end_time(struct sock *sk)
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{
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u64 end_time = ACCESS_ONCE(sk->sk_ll_usec);
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return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + sched_clock();
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}
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/* we don't mind a ~2.5% imprecision
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* sk->sk_ll_usec is a u_int so this can't overflow
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*/
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end_time = (end_time << 10) + sched_clock();
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return end_time;
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/* in poll/select we use the global sysctl_net_ll_poll value */
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static inline u64 ll_end_time(void)
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{
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return ((u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10) + sched_clock();
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}
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static inline bool sk_valid_ll(struct sock *sk)
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@ -62,10 +64,13 @@ static inline bool can_poll_ll(u64 end_time)
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return !time_after64(sched_clock(), end_time);
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}
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/* when used in sock_poll() nonblock is known at compile time to be true
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* so the loop and end_time will be optimized out
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*/
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static inline bool sk_poll_ll(struct sock *sk, int nonblock)
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{
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u64 end_time = nonblock ? 0 : ll_sk_end_time(sk);
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const struct net_device_ops *ops;
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u64 end_time = ll_end_time(sk);
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struct napi_struct *napi;
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int rc = false;
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@ -84,7 +89,6 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock)
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goto out;
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do {
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rc = ops->ndo_ll_poll(napi);
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if (rc == LL_FLUSH_FAILED)
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@ -95,8 +99,8 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock)
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NET_ADD_STATS_BH(sock_net(sk),
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LINUX_MIB_LOWLATENCYRXPACKETS, rc);
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} while (skb_queue_empty(&sk->sk_receive_queue)
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&& can_poll_ll(end_time) && !nonblock);
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} while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
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can_poll_ll(end_time));
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rc = !skb_queue_empty(&sk->sk_receive_queue);
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out:
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@ -118,7 +122,12 @@ static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
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#else /* CONFIG_NET_LL_RX_POLL */
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static inline u64 ll_end_time(struct sock *sk)
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static inline u64 sk_ll_end_time(struct sock *sk)
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{
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return 0;
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}
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static inline u64 ll_end_time(void)
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{
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return 0;
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}
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@ -30,6 +30,8 @@
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#define POLLFREE 0x4000 /* currently only for epoll */
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#define POLL_LL 0x8000
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struct pollfd {
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int fd;
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short events;
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@ -2307,7 +2307,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
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#ifdef CONFIG_NET_LL_RX_POLL
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sk->sk_napi_id = 0;
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sk->sk_ll_usec = sysctl_net_ll_poll;
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sk->sk_ll_usec = sysctl_net_ll_read;
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#endif
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/*
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@ -306,6 +306,14 @@ static struct ctl_table net_core_table[] = {
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.mode = 0644,
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.proc_handler = proc_dointvec
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},
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{
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.procname = "low_latency_read",
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.data = &sysctl_net_ll_read,
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.maxlen = sizeof(unsigned int),
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.mode = 0644,
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.proc_handler = proc_dointvec
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},
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#
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#endif
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#endif /* CONFIG_NET */
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{
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14
net/socket.c
14
net/socket.c
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@ -107,6 +107,7 @@
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#include <net/ll_poll.h>
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#ifdef CONFIG_NET_LL_RX_POLL
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unsigned int sysctl_net_ll_read __read_mostly;
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unsigned int sysctl_net_ll_poll __read_mostly;
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#endif
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@ -1147,13 +1148,24 @@ EXPORT_SYMBOL(sock_create_lite);
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/* No kernel lock held - perfect */
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static unsigned int sock_poll(struct file *file, poll_table *wait)
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{
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unsigned int ll_flag = 0;
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struct socket *sock;
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/*
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* We can't return errors to poll, so it's either yes or no.
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*/
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sock = file->private_data;
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return sock->ops->poll(file, sock, wait);
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if (sk_valid_ll(sock->sk)) {
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/* this socket can poll_ll so tell the system call */
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ll_flag = POLL_LL;
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/* once, only if requested by syscall */
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if (wait && (wait->_key & POLL_LL))
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sk_poll_ll(sock->sk, 1);
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}
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return ll_flag | sock->ops->poll(file, sock, wait);
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}
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static int sock_mmap(struct file *file, struct vm_area_struct *vma)
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