112 lines
4.5 KiB
Diff
112 lines
4.5 KiB
Diff
From 7726f6461eebf2c4a4b129f1c98add25c0b1bee2 Mon Sep 17 00:00:00 2001
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From: Peter Xu <peterx@redhat.com>
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Date: Thu, 29 Jul 2021 07:42:16 -0400
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Subject: [PATCH 12/39] migration: Move bitmap_mutex out of
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migration_bitmap_clear_dirty()
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RH-Author: Miroslav Rezanina <mrezanin@redhat.com>
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RH-MergeRequest: 32: Synchronize with RHEL-AV 8.5 release 27 to RHEL 9
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RH-Commit: [4/15] cc207372dab253a4db3b6d351fa2fb2f442437ad (mrezanin/centos-src-qemu-kvm)
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RH-Bugzilla: 1957194
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RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Igor Mammedov <imammedo@redhat.com>
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RH-Acked-by: Andrew Jones <drjones@redhat.com>
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Taking the mutex every time for each dirty bit to clear is too slow, especially
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we'll take/release even if the dirty bit is cleared. So far it's only used to
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sync with special cases with qemu_guest_free_page_hint() against migration
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thread, nothing really that serious yet. Let's move the lock to be upper.
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There're two callers of migration_bitmap_clear_dirty().
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For migration, move it into ram_save_iterate(). With the help of MAX_WAIT
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logic, we'll only run ram_save_iterate() for no more than 50ms-ish time, so
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taking the lock once there at the entry. It also means any call sites to
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qemu_guest_free_page_hint() can be delayed; but it should be very rare, only
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during migration, and I don't see a problem with it.
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For COLO, move it up to colo_flush_ram_cache(). I think COLO forgot to take
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that lock even when calling ramblock_sync_dirty_bitmap(), where another example
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is migration_bitmap_sync() who took it right. So let the mutex cover both the
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ramblock_sync_dirty_bitmap() and migration_bitmap_clear_dirty() calls.
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It's even possible to drop the lock so we use atomic operations upon rb->bmap
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and the variable migration_dirty_pages. I didn't do it just to still be safe,
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also not predictable whether the frequent atomic ops could bring overhead too
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e.g. on huge vms when it happens very often. When that really comes, we can
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keep a local counter and periodically call atomic ops. Keep it simple for now.
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Cc: Wei Wang <wei.w.wang@intel.com>
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Cc: David Hildenbrand <david@redhat.com>
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Cc: Hailiang Zhang <zhang.zhanghailiang@huawei.com>
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Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Cc: Juan Quintela <quintela@redhat.com>
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Cc: Leonardo Bras Soares Passos <lsoaresp@redhat.com>
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Signed-off-by: Peter Xu <peterx@redhat.com>
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Message-Id: <20210630200805.280905-1-peterx@redhat.com>
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Reviewed-by: Wei Wang <wei.w.wang@intel.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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(cherry picked from commit 63268c4970a5f126cc9af75f3ccb8057abef5ec0)
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Signed-off-by: Peter Xu <peterx@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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migration/ram.c | 13 +++++++++++--
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1 file changed, 11 insertions(+), 2 deletions(-)
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diff --git a/migration/ram.c b/migration/ram.c
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index 4682f3625c..5d64917dce 100644
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--- a/migration/ram.c
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+++ b/migration/ram.c
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@@ -819,8 +819,6 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs,
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{
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bool ret;
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- QEMU_LOCK_GUARD(&rs->bitmap_mutex);
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-
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/*
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* Clear dirty bitmap if needed. This _must_ be called before we
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* send any of the page in the chunk because we need to make sure
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@@ -2869,6 +2867,14 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
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goto out;
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}
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+ /*
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+ * We'll take this lock a little bit long, but it's okay for two reasons.
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+ * Firstly, the only possible other thread to take it is who calls
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+ * qemu_guest_free_page_hint(), which should be rare; secondly, see
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+ * MAX_WAIT (if curious, further see commit 4508bd9ed8053ce) below, which
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+ * guarantees that we'll at least released it in a regular basis.
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+ */
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+ qemu_mutex_lock(&rs->bitmap_mutex);
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WITH_RCU_READ_LOCK_GUARD() {
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if (ram_list.version != rs->last_version) {
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ram_state_reset(rs);
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@@ -2928,6 +2934,7 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
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i++;
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}
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}
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+ qemu_mutex_unlock(&rs->bitmap_mutex);
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/*
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* Must occur before EOS (or any QEMUFile operation)
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@@ -3710,6 +3717,7 @@ void colo_flush_ram_cache(void)
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unsigned long offset = 0;
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memory_global_dirty_log_sync();
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+ qemu_mutex_lock(&ram_state->bitmap_mutex);
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WITH_RCU_READ_LOCK_GUARD() {
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RAMBLOCK_FOREACH_NOT_IGNORED(block) {
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ramblock_sync_dirty_bitmap(ram_state, block);
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@@ -3738,6 +3746,7 @@ void colo_flush_ram_cache(void)
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}
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}
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trace_colo_flush_ram_cache_end();
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+ qemu_mutex_unlock(&ram_state->bitmap_mutex);
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}
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/**
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--
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2.27.0
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