xen: enter/exit lazy_mmu_mode around m2p_override calls
This patch is a significant performance improvement for the m2p_override: about 6% using the gntdev device. Each m2p_add/remove_override call issues a MULTI_grant_table_op and a __flush_tlb_single if kmap_op != NULL. Batching all the calls together is a great performance benefit because it means issuing one hypercall total rather than two hypercall per page. If paravirt_lazy_mode is set PARAVIRT_LAZY_MMU, all these calls are going to be batched together, otherwise they are issued one at a time. Adding arch_enter_lazy_mmu_mode/arch_leave_lazy_mmu_mode around the m2p_add/remove_override calls forces paravirt_lazy_mode to PARAVIRT_LAZY_MMU, therefore makes sure that they are always batched. However it is not safe to call arch_enter_lazy_mmu_mode if we are in interrupt context or if we are already in PARAVIRT_LAZY_MMU mode, so check for both conditions before doing so. Changes in v4: - rebased on 3.4-rc4: all the m2p_override users call gnttab_unmap_refs and gnttab_map_refs; - check whether we are in interrupt context and the lazy_mode we are in before calling arch_enter/leave_lazy_mmu_mode. Changes in v3: - do not call arch_enter/leave_lazy_mmu_mode in xen_blkbk_unmap, that can be called in interrupt context. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> [v5: s/int lazy/bool lazy/] Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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@ -38,6 +38,7 @@
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#include <linux/vmalloc.h>
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#include <linux/uaccess.h>
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#include <linux/io.h>
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#include <linux/hardirq.h>
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#include <xen/xen.h>
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#include <xen/interface/xen.h>
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@ -827,6 +828,7 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
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struct page **pages, unsigned int count)
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{
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int i, ret;
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bool lazy = false;
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pte_t *pte;
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unsigned long mfn;
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@ -837,6 +839,11 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
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if (xen_feature(XENFEAT_auto_translated_physmap))
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return ret;
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if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
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arch_enter_lazy_mmu_mode();
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lazy = true;
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}
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for (i = 0; i < count; i++) {
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/* Do not add to override if the map failed. */
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if (map_ops[i].status)
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@ -855,6 +862,9 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
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return ret;
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}
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if (lazy)
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arch_leave_lazy_mmu_mode();
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return ret;
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}
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EXPORT_SYMBOL_GPL(gnttab_map_refs);
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@ -863,6 +873,7 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
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struct page **pages, unsigned int count, bool clear_pte)
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{
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int i, ret;
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bool lazy = false;
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ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count);
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if (ret)
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@ -871,12 +882,20 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
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if (xen_feature(XENFEAT_auto_translated_physmap))
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return ret;
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if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
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arch_enter_lazy_mmu_mode();
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lazy = true;
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}
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for (i = 0; i < count; i++) {
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ret = m2p_remove_override(pages[i], clear_pte);
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if (ret)
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return ret;
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}
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if (lazy)
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arch_leave_lazy_mmu_mode();
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return ret;
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}
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EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
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