qemu/block/commit.c
Sascha Silbe f14a39ccb9 Improve block job rate limiting for small bandwidth values
ratelimit_calculate_delay() previously reset the accounting every time
slice, no matter how much data had been processed before. This had (at
least) two consequences:

1. The minimum speed is rather large, e.g. 5 MiB/s for commit and stream.

   Not sure if there are real-world use cases where this would be a
   problem. Mirroring and backup over a slow link (e.g. DSL) would
   come to mind, though.

2. Tests for block job operations (e.g. cancel) were rather racy

   All block jobs currently use a time slice of 100ms. That's a
   reasonable value to get smooth output during regular
   operation. However this also meant that the state of block jobs
   changed every 100ms, no matter how low the configured limit was. On
   busy hosts, qemu often transferred additional chunks until the test
   case had a chance to cancel the job.

Fix the block job rate limit code to delay for more than one time
slice to address the above issues. To make it easier to handle
oversized chunks we switch the semantics from returning a delay
_before_ the current request to a delay _after_ the current
request. If necessary, this delay consists of multiple time slice
units.

Since the mirror job sends multiple chunks in one go even if the rate
limit was exceeded in between, we need to keep track of the start of
the current time slice so we can correctly re-compute the delay for
the updated amount of data.

The minimum bandwidth now is 1 data unit per time slice. The block
jobs are currently passing the amount of data transferred in sectors
and using 100ms time slices, so this translates to 5120
bytes/second. With chunk sizes usually being O(512KiB), tests have
plenty of time (O(100s)) to operate on block jobs. The chance of a
race condition now is fairly remote, except possibly on insanely
loaded systems.

Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Message-id: 1467127721-9564-2-git-send-email-silbe@linux.vnet.ibm.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
2016-07-13 13:41:38 +02:00

404 lines
11 KiB
C

/*
* Live block commit
*
* Copyright Red Hat, Inc. 2012
*
* Authors:
* Jeff Cody <jcody@redhat.com>
* Based on stream.c by Stefan Hajnoczi
*
* This work is licensed under the terms of the GNU LGPL, version 2 or later.
* See the COPYING.LIB file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "trace.h"
#include "block/block_int.h"
#include "block/blockjob.h"
#include "qapi/error.h"
#include "qapi/qmp/qerror.h"
#include "qemu/ratelimit.h"
#include "sysemu/block-backend.h"
enum {
/*
* Size of data buffer for populating the image file. This should be large
* enough to process multiple clusters in a single call, so that populating
* contiguous regions of the image is efficient.
*/
COMMIT_BUFFER_SIZE = 512 * 1024, /* in bytes */
};
#define SLICE_TIME 100000000ULL /* ns */
typedef struct CommitBlockJob {
BlockJob common;
RateLimit limit;
BlockDriverState *active;
BlockBackend *top;
BlockBackend *base;
BlockdevOnError on_error;
int base_flags;
int orig_overlay_flags;
char *backing_file_str;
} CommitBlockJob;
static int coroutine_fn commit_populate(BlockBackend *bs, BlockBackend *base,
int64_t sector_num, int nb_sectors,
void *buf)
{
int ret = 0;
QEMUIOVector qiov;
struct iovec iov = {
.iov_base = buf,
.iov_len = nb_sectors * BDRV_SECTOR_SIZE,
};
qemu_iovec_init_external(&qiov, &iov, 1);
ret = blk_co_preadv(bs, sector_num * BDRV_SECTOR_SIZE,
qiov.size, &qiov, 0);
if (ret < 0) {
return ret;
}
ret = blk_co_pwritev(base, sector_num * BDRV_SECTOR_SIZE,
qiov.size, &qiov, 0);
if (ret < 0) {
return ret;
}
return 0;
}
typedef struct {
int ret;
} CommitCompleteData;
static void commit_complete(BlockJob *job, void *opaque)
{
CommitBlockJob *s = container_of(job, CommitBlockJob, common);
CommitCompleteData *data = opaque;
BlockDriverState *active = s->active;
BlockDriverState *top = blk_bs(s->top);
BlockDriverState *base = blk_bs(s->base);
BlockDriverState *overlay_bs;
int ret = data->ret;
if (!block_job_is_cancelled(&s->common) && ret == 0) {
/* success */
ret = bdrv_drop_intermediate(active, top, base, s->backing_file_str);
}
/* restore base open flags here if appropriate (e.g., change the base back
* to r/o). These reopens do not need to be atomic, since we won't abort
* even on failure here */
if (s->base_flags != bdrv_get_flags(base)) {
bdrv_reopen(base, s->base_flags, NULL);
}
overlay_bs = bdrv_find_overlay(active, top);
if (overlay_bs && s->orig_overlay_flags != bdrv_get_flags(overlay_bs)) {
bdrv_reopen(overlay_bs, s->orig_overlay_flags, NULL);
}
g_free(s->backing_file_str);
blk_unref(s->top);
blk_unref(s->base);
block_job_completed(&s->common, ret);
g_free(data);
}
static void coroutine_fn commit_run(void *opaque)
{
CommitBlockJob *s = opaque;
CommitCompleteData *data;
int64_t sector_num, end;
uint64_t delay_ns = 0;
int ret = 0;
int n = 0;
void *buf = NULL;
int bytes_written = 0;
int64_t base_len;
ret = s->common.len = blk_getlength(s->top);
if (s->common.len < 0) {
goto out;
}
ret = base_len = blk_getlength(s->base);
if (base_len < 0) {
goto out;
}
if (base_len < s->common.len) {
ret = blk_truncate(s->base, s->common.len);
if (ret) {
goto out;
}
}
end = s->common.len >> BDRV_SECTOR_BITS;
buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
for (sector_num = 0; sector_num < end; sector_num += n) {
bool copy;
/* Note that even when no rate limit is applied we need to yield
* with no pending I/O here so that bdrv_drain_all() returns.
*/
block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, delay_ns);
if (block_job_is_cancelled(&s->common)) {
break;
}
/* Copy if allocated above the base */
ret = bdrv_is_allocated_above(blk_bs(s->top), blk_bs(s->base),
sector_num,
COMMIT_BUFFER_SIZE / BDRV_SECTOR_SIZE,
&n);
copy = (ret == 1);
trace_commit_one_iteration(s, sector_num, n, ret);
if (copy) {
ret = commit_populate(s->top, s->base, sector_num, n, buf);
bytes_written += n * BDRV_SECTOR_SIZE;
}
if (ret < 0) {
BlockErrorAction action =
block_job_error_action(&s->common, false, s->on_error, -ret);
if (action == BLOCK_ERROR_ACTION_REPORT) {
goto out;
} else {
n = 0;
continue;
}
}
/* Publish progress */
s->common.offset += n * BDRV_SECTOR_SIZE;
if (copy && s->common.speed) {
delay_ns = ratelimit_calculate_delay(&s->limit, n);
}
}
ret = 0;
out:
qemu_vfree(buf);
data = g_malloc(sizeof(*data));
data->ret = ret;
block_job_defer_to_main_loop(&s->common, commit_complete, data);
}
static void commit_set_speed(BlockJob *job, int64_t speed, Error **errp)
{
CommitBlockJob *s = container_of(job, CommitBlockJob, common);
if (speed < 0) {
error_setg(errp, QERR_INVALID_PARAMETER, "speed");
return;
}
ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
}
static const BlockJobDriver commit_job_driver = {
.instance_size = sizeof(CommitBlockJob),
.job_type = BLOCK_JOB_TYPE_COMMIT,
.set_speed = commit_set_speed,
};
void commit_start(const char *job_id, BlockDriverState *bs,
BlockDriverState *base, BlockDriverState *top, int64_t speed,
BlockdevOnError on_error, BlockCompletionFunc *cb,
void *opaque, const char *backing_file_str, Error **errp)
{
CommitBlockJob *s;
BlockReopenQueue *reopen_queue = NULL;
int orig_overlay_flags;
int orig_base_flags;
BlockDriverState *overlay_bs;
Error *local_err = NULL;
assert(top != bs);
if (top == base) {
error_setg(errp, "Invalid files for merge: top and base are the same");
return;
}
overlay_bs = bdrv_find_overlay(bs, top);
if (overlay_bs == NULL) {
error_setg(errp, "Could not find overlay image for %s:", top->filename);
return;
}
s = block_job_create(job_id, &commit_job_driver, bs, speed,
cb, opaque, errp);
if (!s) {
return;
}
orig_base_flags = bdrv_get_flags(base);
orig_overlay_flags = bdrv_get_flags(overlay_bs);
/* convert base & overlay_bs to r/w, if necessary */
if (!(orig_overlay_flags & BDRV_O_RDWR)) {
reopen_queue = bdrv_reopen_queue(reopen_queue, overlay_bs, NULL,
orig_overlay_flags | BDRV_O_RDWR);
}
if (!(orig_base_flags & BDRV_O_RDWR)) {
reopen_queue = bdrv_reopen_queue(reopen_queue, base, NULL,
orig_base_flags | BDRV_O_RDWR);
}
if (reopen_queue) {
bdrv_reopen_multiple(reopen_queue, &local_err);
if (local_err != NULL) {
error_propagate(errp, local_err);
block_job_unref(&s->common);
return;
}
}
s->base = blk_new();
blk_insert_bs(s->base, base);
s->top = blk_new();
blk_insert_bs(s->top, top);
s->active = bs;
s->base_flags = orig_base_flags;
s->orig_overlay_flags = orig_overlay_flags;
s->backing_file_str = g_strdup(backing_file_str);
s->on_error = on_error;
s->common.co = qemu_coroutine_create(commit_run, s);
trace_commit_start(bs, base, top, s, s->common.co, opaque);
qemu_coroutine_enter(s->common.co);
}
#define COMMIT_BUF_SECTORS 2048
/* commit COW file into the raw image */
int bdrv_commit(BlockDriverState *bs)
{
BlockBackend *src, *backing;
BlockDriver *drv = bs->drv;
int64_t sector, total_sectors, length, backing_length;
int n, ro, open_flags;
int ret = 0;
uint8_t *buf = NULL;
if (!drv)
return -ENOMEDIUM;
if (!bs->backing) {
return -ENOTSUP;
}
if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, NULL) ||
bdrv_op_is_blocked(bs->backing->bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL)) {
return -EBUSY;
}
ro = bs->backing->bs->read_only;
open_flags = bs->backing->bs->open_flags;
if (ro) {
if (bdrv_reopen(bs->backing->bs, open_flags | BDRV_O_RDWR, NULL)) {
return -EACCES;
}
}
src = blk_new();
blk_insert_bs(src, bs);
backing = blk_new();
blk_insert_bs(backing, bs->backing->bs);
length = blk_getlength(src);
if (length < 0) {
ret = length;
goto ro_cleanup;
}
backing_length = blk_getlength(backing);
if (backing_length < 0) {
ret = backing_length;
goto ro_cleanup;
}
/* If our top snapshot is larger than the backing file image,
* grow the backing file image if possible. If not possible,
* we must return an error */
if (length > backing_length) {
ret = blk_truncate(backing, length);
if (ret < 0) {
goto ro_cleanup;
}
}
total_sectors = length >> BDRV_SECTOR_BITS;
/* blk_try_blockalign() for src will choose an alignment that works for
* backing as well, so no need to compare the alignment manually. */
buf = blk_try_blockalign(src, COMMIT_BUF_SECTORS * BDRV_SECTOR_SIZE);
if (buf == NULL) {
ret = -ENOMEM;
goto ro_cleanup;
}
for (sector = 0; sector < total_sectors; sector += n) {
ret = bdrv_is_allocated(bs, sector, COMMIT_BUF_SECTORS, &n);
if (ret < 0) {
goto ro_cleanup;
}
if (ret) {
ret = blk_pread(src, sector * BDRV_SECTOR_SIZE, buf,
n * BDRV_SECTOR_SIZE);
if (ret < 0) {
goto ro_cleanup;
}
ret = blk_pwrite(backing, sector * BDRV_SECTOR_SIZE, buf,
n * BDRV_SECTOR_SIZE, 0);
if (ret < 0) {
goto ro_cleanup;
}
}
}
if (drv->bdrv_make_empty) {
ret = drv->bdrv_make_empty(bs);
if (ret < 0) {
goto ro_cleanup;
}
blk_flush(src);
}
/*
* Make sure all data we wrote to the backing device is actually
* stable on disk.
*/
blk_flush(backing);
ret = 0;
ro_cleanup:
qemu_vfree(buf);
blk_unref(src);
blk_unref(backing);
if (ro) {
/* ignoring error return here */
bdrv_reopen(bs->backing->bs, open_flags & ~BDRV_O_RDWR, NULL);
}
return ret;
}