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