[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 2/2] grant_table: convert grant table rwlock to percpu rwlock
The per domain grant table read lock suffers from significant contention when performance multi-queue block or network IO due to the parallel grant map/unmaps/copies occuring on the DomU's grant table. On multi-socket systems, the contention results in the locked compare swap operation failing frequently which results in a tight loop of retries of the compare swap operation. As the coherency fabric can only support a specific rate of compare swap operations for a particular data location then taking the read lock itself becomes a bottleneck for grant operations. Standard rwlock performance of a single VIF VM-VM transfer with 16 queues configured was limited to approxmiately 10 gbit/s on a 2 socket Haswell-EP host. Percpu rwlock performance with the same configuration is approximately 50 gbit/s. Oprofile was used to determine the initial overhead of the read-write locks and to confirm the overhead was dramatically reduced by the percpu rwlocks. Signed-off-by: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx> --- xen/arch/arm/mm.c | 5 ++- xen/arch/x86/mm.c | 5 ++- xen/common/grant_table.c | 100 ++++++++++++++++++++++-------------------- xen/include/xen/grant_table.h | 4 ++ 4 files changed, 62 insertions(+), 52 deletions(-) diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 8b6d915..596cabf 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -1055,7 +1055,8 @@ int xenmem_add_to_physmap_one( switch ( space ) { case XENMAPSPACE_grant_table: - write_lock(&d->grant_table->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, + &d->grant_table->lock); if ( d->grant_table->gt_version == 0 ) d->grant_table->gt_version = 1; @@ -1085,7 +1086,7 @@ int xenmem_add_to_physmap_one( t = p2m_ram_rw; - write_unlock(&d->grant_table->lock); + percpu_write_unlock(&grant_rwlock_barrier, &d->grant_table->lock); break; case XENMAPSPACE_shared_info: if ( idx != 0 ) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 92df36f..2a6fe61 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -4654,7 +4654,8 @@ int xenmem_add_to_physmap_one( mfn = virt_to_mfn(d->shared_info); break; case XENMAPSPACE_grant_table: - write_lock(&d->grant_table->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, + &d->grant_table->lock); if ( d->grant_table->gt_version == 0 ) d->grant_table->gt_version = 1; @@ -4676,7 +4677,7 @@ int xenmem_add_to_physmap_one( mfn = virt_to_mfn(d->grant_table->shared_raw[idx]); } - write_unlock(&d->grant_table->lock); + percpu_write_unlock(&grant_rwlock_barrier, &d->grant_table->lock); break; case XENMAPSPACE_gmfn_range: case XENMAPSPACE_gmfn: diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c index 5d52d1e..8d19d2a 100644 --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -178,6 +178,10 @@ struct active_grant_entry { #define _active_entry(t, e) \ ((t)->active[(e)/ACGNT_PER_PAGE][(e)%ACGNT_PER_PAGE]) +bool_t grant_rwlock_barrier; + +DEFINE_PER_CPU(rwlock_t *, grant_rwlock); + static inline void gnttab_flush_tlb(const struct domain *d) { if ( !paging_mode_external(d) ) @@ -270,23 +274,23 @@ double_gt_lock(struct grant_table *lgt, struct grant_table *rgt) */ if ( lgt < rgt ) { - write_lock(&lgt->lock); - write_lock(&rgt->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &lgt->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); } else { if ( lgt != rgt ) - write_lock(&rgt->lock); - write_lock(&lgt->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &lgt->lock); } } static inline void double_gt_unlock(struct grant_table *lgt, struct grant_table *rgt) { - write_unlock(&lgt->lock); + percpu_write_unlock(&grant_rwlock_barrier, &lgt->lock); if ( lgt != rgt ) - write_unlock(&rgt->lock); + percpu_write_unlock(&grant_rwlock_barrier, &rgt->lock); } static inline int @@ -796,7 +800,7 @@ __gnttab_map_grant_ref( } rgt = rd->grant_table; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); /* Bounds check on the grant ref */ if ( unlikely(op->ref >= nr_grant_entries(rgt))) @@ -859,7 +863,7 @@ __gnttab_map_grant_ref( cache_flags = (shah->flags & (GTF_PAT | GTF_PWT | GTF_PCD) ); active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); /* pg may be set, with a refcount included, from __get_paged_frame */ if ( !pg ) @@ -1006,7 +1010,7 @@ __gnttab_map_grant_ref( put_page(pg); } - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); act = active_entry_acquire(rgt, op->ref); @@ -1029,7 +1033,7 @@ __gnttab_map_grant_ref( active_entry_release(act); unlock_out: - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); op->status = rc; put_maptrack_handle(lgt, handle); rcu_unlock_domain(rd); @@ -1080,18 +1084,18 @@ __gnttab_unmap_common( op->map = &maptrack_entry(lgt, op->handle); - read_lock(&lgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &lgt->lock); if ( unlikely(!read_atomic(&op->map->flags)) ) { - read_unlock(&lgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); gdprintk(XENLOG_INFO, "Zero flags for handle (%d).\n", op->handle); op->status = GNTST_bad_handle; return; } dom = op->map->domid; - read_unlock(&lgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); if ( unlikely((rd = rcu_lock_domain_by_id(dom)) == NULL) ) { @@ -1113,7 +1117,7 @@ __gnttab_unmap_common( rgt = rd->grant_table; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); op->flags = read_atomic(&op->map->flags); if ( unlikely(!op->flags) || unlikely(op->map->domid != dom) ) @@ -1165,7 +1169,7 @@ __gnttab_unmap_common( act_release_out: active_entry_release(act); unmap_out: - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); if ( rc == GNTST_okay && gnttab_need_iommu_mapping(ld) ) { @@ -1220,7 +1224,7 @@ __gnttab_unmap_common_complete(struct gnttab_unmap_common *op) rcu_lock_domain(rd); rgt = rd->grant_table; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); if ( rgt->gt_version == 0 ) goto unlock_out; @@ -1286,7 +1290,7 @@ __gnttab_unmap_common_complete(struct gnttab_unmap_common *op) act_release_out: active_entry_release(act); unlock_out: - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); if ( put_handle ) { @@ -1585,7 +1589,7 @@ gnttab_setup_table( } gt = d->grant_table; - write_lock(>->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, >->lock); if ( gt->gt_version == 0 ) gt->gt_version = 1; @@ -1613,7 +1617,7 @@ gnttab_setup_table( } out3: - write_unlock(>->lock); + percpu_write_unlock(&grant_rwlock_barrier, >->lock); out2: rcu_unlock_domain(d); out1: @@ -1655,13 +1659,13 @@ gnttab_query_size( goto query_out_unlock; } - read_lock(&d->grant_table->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &d->grant_table->lock); op.nr_frames = nr_grant_frames(d->grant_table); op.max_nr_frames = max_grant_frames; op.status = GNTST_okay; - read_unlock(&d->grant_table->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); query_out_unlock: @@ -1687,7 +1691,7 @@ gnttab_prepare_for_transfer( union grant_combo scombo, prev_scombo, new_scombo; int retries = 0; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); if ( unlikely(ref >= nr_grant_entries(rgt)) ) { @@ -1730,11 +1734,11 @@ gnttab_prepare_for_transfer( scombo = prev_scombo; } - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); return 1; fail: - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); return 0; } @@ -1925,7 +1929,7 @@ gnttab_transfer( TRACE_1D(TRC_MEM_PAGE_GRANT_TRANSFER, e->domain_id); /* Tell the guest about its new page frame. */ - read_lock(&e->grant_table->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &e->grant_table->lock); act = active_entry_acquire(e->grant_table, gop.ref); if ( e->grant_table->gt_version == 1 ) @@ -1949,7 +1953,7 @@ gnttab_transfer( GTF_transfer_completed; active_entry_release(act); - read_unlock(&e->grant_table->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); rcu_unlock_domain(e); @@ -1987,7 +1991,7 @@ __release_grant_for_copy( released_read = 0; released_write = 0; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); act = active_entry_acquire(rgt, gref); sha = shared_entry_header(rgt, gref); @@ -2029,7 +2033,7 @@ __release_grant_for_copy( } active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); if ( td != rd ) { @@ -2086,7 +2090,7 @@ __acquire_grant_for_copy( *page = NULL; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); if ( unlikely(gref >= nr_grant_entries(rgt)) ) PIN_FAIL(gt_unlock_out, GNTST_bad_gntref, @@ -2168,20 +2172,20 @@ __acquire_grant_for_copy( * here and reacquire */ active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); rc = __acquire_grant_for_copy(td, trans_gref, rd->domain_id, readonly, &grant_frame, page, &trans_page_off, &trans_length, 0); - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); act = active_entry_acquire(rgt, gref); if ( rc != GNTST_okay ) { __fixup_status_for_copy_pin(act, status); rcu_unlock_domain(td); active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); return rc; } @@ -2194,7 +2198,7 @@ __acquire_grant_for_copy( __fixup_status_for_copy_pin(act, status); rcu_unlock_domain(td); active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); put_page(*page); return __acquire_grant_for_copy(rd, gref, ldom, readonly, frame, page, page_off, length, @@ -2258,7 +2262,7 @@ __acquire_grant_for_copy( *frame = act->frame; active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); return rc; unlock_out_clear: @@ -2273,7 +2277,7 @@ __acquire_grant_for_copy( active_entry_release(act); gt_unlock_out: - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); return rc; } @@ -2589,7 +2593,7 @@ gnttab_set_version(XEN_GUEST_HANDLE_PARAM(gnttab_set_version_t) uop) if ( gt->gt_version == op.version ) goto out; - write_lock(>->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, >->lock); /* * Make sure that the grant table isn't currently in use when we * change the version number, except for the first 8 entries which @@ -2702,7 +2706,7 @@ gnttab_set_version(XEN_GUEST_HANDLE_PARAM(gnttab_set_version_t) uop) gt->gt_version = op.version; out_unlock: - write_unlock(>->lock); + percpu_write_unlock(&grant_rwlock_barrier, >->lock); out: op.version = gt->gt_version; @@ -2758,7 +2762,7 @@ gnttab_get_status_frames(XEN_GUEST_HANDLE_PARAM(gnttab_get_status_frames_t) uop, op.status = GNTST_okay; - read_lock(>->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, >->lock); for ( i = 0; i < op.nr_frames; i++ ) { @@ -2767,7 +2771,7 @@ gnttab_get_status_frames(XEN_GUEST_HANDLE_PARAM(gnttab_get_status_frames_t) uop, op.status = GNTST_bad_virt_addr; } - read_unlock(>->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); out2: rcu_unlock_domain(d); out1: @@ -2817,7 +2821,7 @@ __gnttab_swap_grant_ref(grant_ref_t ref_a, grant_ref_t ref_b) struct active_grant_entry *act_b = NULL; s16 rc = GNTST_okay; - write_lock(>->lock); + percpu_write_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, >->lock); /* Bounds check on the grant refs */ if ( unlikely(ref_a >= nr_grant_entries(d->grant_table))) @@ -2865,7 +2869,7 @@ out: active_entry_release(act_b); if ( act_a != NULL ) active_entry_release(act_a); - write_unlock(>->lock); + percpu_write_unlock(&grant_rwlock_barrier, >->lock); rcu_unlock_domain(d); @@ -2936,12 +2940,12 @@ static int __gnttab_cache_flush(gnttab_cache_flush_t *cflush, if ( d != owner ) { - read_lock(&owner->grant_table->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &owner->grant_table->lock); ret = grant_map_exists(d, owner->grant_table, mfn, ref_count); if ( ret != 0 ) { - read_unlock(&owner->grant_table->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); rcu_unlock_domain(d); put_page(page); return ret; @@ -2961,7 +2965,7 @@ static int __gnttab_cache_flush(gnttab_cache_flush_t *cflush, ret = 0; if ( d != owner ) - read_unlock(&owner->grant_table->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); unmap_domain_page(v); put_page(page); @@ -3282,7 +3286,7 @@ gnttab_release_mappings( } rgt = rd->grant_table; - read_lock(&rgt->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, &rgt->lock); act = active_entry_acquire(rgt, ref); sha = shared_entry_header(rgt, ref); @@ -3343,7 +3347,7 @@ gnttab_release_mappings( gnttab_clear_flag(_GTF_reading, status); active_entry_release(act); - read_unlock(&rgt->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); rcu_unlock_domain(rd); @@ -3432,7 +3436,7 @@ static void gnttab_usage_print(struct domain *rd) printk(" -------- active -------- -------- shared --------\n"); printk("[ref] localdom mfn pin localdom gmfn flags\n"); - read_lock(>->lock); + percpu_read_lock(&get_per_cpu_var(grant_rwlock), &grant_rwlock_barrier, >->lock); for ( ref = 0; ref != nr_grant_entries(gt); ref++ ) { @@ -3475,7 +3479,7 @@ static void gnttab_usage_print(struct domain *rd) active_entry_release(act); } - read_unlock(>->lock); + percpu_read_unlock(&get_per_cpu_var(grant_rwlock)); if ( first ) printk("grant-table for remote domain:%5d ... " diff --git a/xen/include/xen/grant_table.h b/xen/include/xen/grant_table.h index 1c29cee..6056d3e 100644 --- a/xen/include/xen/grant_table.h +++ b/xen/include/xen/grant_table.h @@ -51,6 +51,10 @@ /* The maximum size of a grant table. */ extern unsigned int max_grant_frames; +extern bool_t grant_rwlock_barrier; + +DECLARE_PER_CPU(rwlock_t *, grant_rwlock); + /* Per-domain grant information. */ struct grant_table { /* -- 1.7.12.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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