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add patch to avoid huge snapshot performance regression

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Taking a snapshot became prohibitively slow because of the
migration_transferred_bytes() call in migration_rate_exceeded() [0].

This also applied to the async snapshot taking in Proxmox VE, so
work around the issue until it is fixed upstream.

[0]: https://gitlab.com/qemu-project/qemu/-/issues/1821

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
This commit is contained in:
Fiona Ebner 2023-10-17 14:10:11 +02:00 committed by Thomas Lamprecht
parent 03ff63aa61
commit a36bda146c
2 changed files with 58 additions and 0 deletions
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57
debian/patches/extra/0007-migration-states-workaround-snapshot-performance-reg.patch vendored Normal file
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@ -0,0 +1,57 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Fiona Ebner <f.ebner@proxmox.com>
Date: Thu, 28 Sep 2023 11:19:14 +0200
Subject: [PATCH] migration states: workaround snapshot performance regression
Commit 813cd616 ("migration: Use migration_transferred_bytes() to
calculate rate_limit") introduced a prohibitive performance regression
when taking a snapshot [0]. The reason turns out to be the flushing
done by migration_transferred_bytes()
Just use a _noflush version of the relevant function as a workaround
until upstream fixes the issue. This is inspired by a not-applied
upstream series [1], but doing the very minimum to avoid the
regression.
[0]: https://gitlab.com/qemu-project/qemu/-/issues/1821
[1]: https://lists.nongnu.org/archive/html/qemu-devel/2023-05/msg07708.html
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
migration/migration-stats.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/migration/migration-stats.c b/migration/migration-stats.c
index 095d6d75bb..8073c8ebaa 100644
--- a/migration/migration-stats.c
+++ b/migration/migration-stats.c
@@ -18,6 +18,20 @@
MigrationAtomicStats mig_stats;
+/*
+ * Same as migration_transferred_bytes below, but using the _noflush
+ * variant of qemu_file_transferred() to avoid a performance
+ * regression in migration_rate_exceeded().
+ */
+static uint64_t migration_transferred_bytes_noflush(QEMUFile *f)
+{
+ uint64_t multifd = stat64_get(&mig_stats.multifd_bytes);
+ uint64_t qemu_file = qemu_file_transferred_noflush(f);
+
+ trace_migration_transferred_bytes(qemu_file, multifd);
+ return qemu_file + multifd;
+}
+
bool migration_rate_exceeded(QEMUFile *f)
{
if (qemu_file_get_error(f)) {
@@ -25,7 +39,7 @@ bool migration_rate_exceeded(QEMUFile *f)
}
uint64_t rate_limit_start = stat64_get(&mig_stats.rate_limit_start);
- uint64_t rate_limit_current = migration_transferred_bytes(f);
+ uint64_t rate_limit_current = migration_transferred_bytes_noflush(f);
uint64_t rate_limit_used = rate_limit_current - rate_limit_start;
uint64_t rate_limit_max = stat64_get(&mig_stats.rate_limit_max);

1
debian/patches/series vendored
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@ -4,6 +4,7 @@ extra/0003-ide-avoid-potential-deadlock-when-draining-during-tr.patch
extra/0004-migration-block-dirty-bitmap-fix-loading-bitmap-when.patch
extra/0005-hw-ide-reset-cancel-async-DMA-operation-before-reset.patch
extra/0006-Revert-Revert-graph-lock-Disable-locking-for-now.patch
extra/0007-migration-states-workaround-snapshot-performance-reg.patch
bitmap-mirror/0001-drive-mirror-add-support-for-sync-bitmap-mode-never.patch
bitmap-mirror/0002-drive-mirror-add-support-for-conditional-and-always-.patch
bitmap-mirror/0003-mirror-add-check-for-bitmap-mode-without-bitmap.patch