From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-devel@nongnu.org
Cc: eesposit@redhat.com, stefanha@redhat.com, qemu-block@nongnu.org
Subject: [PATCH] ratelimit: protect with a mutex
Date: Tue, 13 Apr 2021 14:55:33 +0200 [thread overview]
Message-ID: <20210413125533.217440-1-pbonzini@redhat.com> (raw)
Right now, rate limiting is protected by the AioContext mutex, which is
taken for example both by the block jobs and by qmp_block_job_set_speed
(via find_block_job).
We would like to remove the dependency of block layer code on the
AioContext mutex, since most drivers and the core I/O code are already
not relying on it. However, there is no existing lock that can easily
be taken by both ratelimit_set_speed and ratelimit_calculate_delay,
especially because the latter might run in coroutine context (and
therefore under a CoMutex) but the former will not.
Since concurrent calls to ratelimit_calculate_delay are not possible,
one idea could be to use a seqlock to get a snapshot of slice_ns and
slice_quota. But for now keep it simple, and just add a mutex to the
RateLimit struct; block jobs are generally not performance critical to
the point of optimizing the clock cycles spent in synchronization.
This also requires the introduction of init/destroy functions, so
add them to the two users of ratelimit.h.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
block/block-copy.c | 2 ++
blockjob.c | 3 +++
include/qemu/ratelimit.h | 14 ++++++++++++++
3 files changed, 19 insertions(+)
diff --git a/block/block-copy.c b/block/block-copy.c
index 39ae481c8b..9b4af00614 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -230,6 +230,7 @@ void block_copy_state_free(BlockCopyState *s)
return;
}
+ ratelimit_destroy(&s->rate_limit);
bdrv_release_dirty_bitmap(s->copy_bitmap);
shres_destroy(s->mem);
g_free(s);
@@ -289,6 +290,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
s->copy_size = MAX(s->cluster_size, BLOCK_COPY_MAX_BUFFER);
}
+ ratelimit_init(&s->rate_limit);
QLIST_INIT(&s->tasks);
QLIST_INIT(&s->calls);
diff --git a/blockjob.c b/blockjob.c
index 207e8c7fd9..46f15befe8 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -87,6 +87,7 @@ void block_job_free(Job *job)
block_job_remove_all_bdrv(bjob);
blk_unref(bjob->blk);
+ ratelimit_destroy(&bjob->limit);
error_free(bjob->blocker);
}
@@ -435,6 +436,8 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
assert(job->job.driver->free == &block_job_free);
assert(job->job.driver->user_resume == &block_job_user_resume);
+ ratelimit_init(&job->limit);
+
job->blk = blk;
job->finalize_cancelled_notifier.notify = block_job_event_cancelled;
diff --git a/include/qemu/ratelimit.h b/include/qemu/ratelimit.h
index 01da8d63f1..003ea6d5a3 100644
--- a/include/qemu/ratelimit.h
+++ b/include/qemu/ratelimit.h
@@ -14,9 +14,11 @@
#ifndef QEMU_RATELIMIT_H
#define QEMU_RATELIMIT_H
+#include "qemu/lockable.h"
#include "qemu/timer.h"
typedef struct {
+ QemuMutex lock;
int64_t slice_start_time;
int64_t slice_end_time;
uint64_t slice_quota;
@@ -40,6 +42,7 @@ static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
double delay_slices;
+ QEMU_LOCK_GUARD(&limit->lock);
assert(limit->slice_quota && limit->slice_ns);
if (limit->slice_end_time < now) {
@@ -65,9 +68,20 @@ static inline int64_t ratelimit_calculate_delay(RateLimit *limit, uint64_t n)
return limit->slice_end_time - now;
}
+static inline void ratelimit_init(RateLimit *limit)
+{
+ qemu_mutex_init(&limit->lock);
+}
+
+static inline void ratelimit_destroy(RateLimit *limit)
+{
+ qemu_mutex_destroy(&limit->lock);
+}
+
static inline void ratelimit_set_speed(RateLimit *limit, uint64_t speed,
uint64_t slice_ns)
{
+ QEMU_LOCK_GUARD(&limit->lock);
limit->slice_ns = slice_ns;
limit->slice_quota = MAX(((double)speed * slice_ns) / 1000000000ULL, 1);
}
--
2.30.1
next reply other threads:[~2021-04-13 12:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 12:55 Paolo Bonzini [this message]
2021-04-14 10:46 ` [PATCH] ratelimit: protect with a mutex Stefan Hajnoczi
2021-04-14 11:22 ` Emanuele Giuseppe Esposito
2021-05-10 9:51 ` Vladimir Sementsov-Ogievskiy
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