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Re: [Qemu-devel] [PATCH] block/mirror: change the semantic of 'force' of
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [PATCH] block/mirror: change the semantic of 'force' of block-job-cancel |
Date: |
Tue, 30 Jan 2018 15:39:21 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 |
On 01/30/2018 03:18 PM, John Snow wrote:
>
>
> On 01/30/2018 03:38 AM, Liang Li wrote:
>> When doing drive mirror to a low speed shared storage, if there was heavy
>> BLK IO write workload in VM after the 'ready' event, drive mirror block job
>> can't be canceled immediately, it would keep running until the heavy BLK IO
>> workload stopped in the VM.
>>
>> Because libvirt depends on block-job-cancel for block live migration, the
>> current block-job-cancel has the semantic to make sure data is in sync after
>> the 'ready' event. This semantic can't meet some requirement, for example,
>> people may use drive mirror for realtime backup while need the ability of
>> block live migration. If drive mirror can't not be cancelled immediately,
>> it means block live migration need to wait, because libvirt make use drive
>> mirror to implement block live migration and only one drive mirror block
>> job is allowed at the same time for a give block dev.
>>
>> We need a new interface for 'force cancel', which could quit block job
>> immediately if don't care about whether data is in sync or not.
>>
>> 'force' is not used by libvirt currently, to make things simple, change
>> it's semantic slightly, hope it will not break some use case which need its
>> original semantic.
>>
>> Cc: Paolo Bonzini <address@hidden>
>> Cc: Jeff Cody <address@hidden>
>> Cc: Kevin Wolf <address@hidden>
>> Cc: Max Reitz <address@hidden>
>> Cc: Eric Blake <address@hidden>
>> Cc: John Snow <address@hidden>
>> Reported-by: Huaitong Han <address@hidden>
>> Signed-off-by: Huaitong Han <address@hidden>
>> Signed-off-by: Liang Li <address@hidden>
>> ---
>> block/mirror.c | 9 +++------
>> blockdev.c | 4 ++--
>> blockjob.c | 11 ++++++-----
>> hmp-commands.hx | 3 ++-
>> include/block/blockjob.h | 9 ++++++++-
>> qapi/block-core.json | 6 ++++--
>> tests/test-blockjob-txn.c | 8 ++++----
>> 7 files changed, 29 insertions(+), 21 deletions(-)
>>
>> diff --git a/block/mirror.c b/block/mirror.c
>> index c9badc1..c22dff9 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -869,11 +869,8 @@ static void coroutine_fn mirror_run(void *opaque)
>>
>> ret = 0;
>> trace_mirror_before_sleep(s, cnt, s->synced, delay_ns);
>> - if (!s->synced) {
>> - block_job_sleep_ns(&s->common, delay_ns);
>> - if (block_job_is_cancelled(&s->common)) {
>> - break;
>> - }
>> + if (block_job_is_cancelled(&s->common) && s->common.force) {
>> + break;
>
> what's the justification for removing the sleep in the case that
> !s->synced && !block_job_is_cancelled(...) ?
>
>> } else if (!should_complete) {
>> delay_ns = (s->in_flight == 0 && cnt == 0 ? SLICE_TIME : 0);
>> block_job_sleep_ns(&s->common, delay_ns);
>> @@ -887,7 +884,7 @@ immediate_exit:
>> * or it was cancelled prematurely so that we do not guarantee that
>> * the target is a copy of the source.
>> */
>> - assert(ret < 0 || (!s->synced &&
>> block_job_is_cancelled(&s->common)));
>> + assert(ret < 0 || block_job_is_cancelled(&s->common));
>
> This assertion gets weaker in the case where force isn't provided, is
> that desired?
>
>> assert(need_drain);
>> mirror_wait_for_all_io(s);
>> }
>> diff --git a/blockdev.c b/blockdev.c
>> index 8e977ee..039f156 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -145,7 +145,7 @@ void blockdev_mark_auto_del(BlockBackend *blk)
>> aio_context_acquire(aio_context);
>>
>> if (bs->job) {
>> - block_job_cancel(bs->job);
>> + block_job_cancel(bs->job, false);
>> }
>>
>> aio_context_release(aio_context);
>> @@ -3802,7 +3802,7 @@ void qmp_block_job_cancel(const char *device,
>> }
>>
>> trace_qmp_block_job_cancel(job);
>> - block_job_cancel(job);
>> + block_job_cancel(job, force);
>> out:
>> aio_context_release(aio_context);
>> }
>> diff --git a/blockjob.c b/blockjob.c
>> index f5cea84..0aacb50 100644
>> --- a/blockjob.c
>> +++ b/blockjob.c
>> @@ -365,7 +365,7 @@ static void block_job_completed_single(BlockJob *job)
>> block_job_unref(job);
>> }
>>
>> -static void block_job_cancel_async(BlockJob *job)
>> +static void block_job_cancel_async(BlockJob *job, bool force)
>> {
>> if (job->iostatus != BLOCK_DEVICE_IO_STATUS_OK) {
>> block_job_iostatus_reset(job);
>> @@ -376,6 +376,7 @@ static void block_job_cancel_async(BlockJob *job)
>> job->pause_count--;
>> }
>> job->cancelled = true;
>> + job->force = force;
>> }
>>
>
> I suppose this is okay; we're setting a permanent property of the job as
> part of a limited operation.
>
> Granted, the job should disappear afterwards, so it should never
> conflict, but it made me wonder for a moment.
>
> What happens if we cancel with force = true and then immediately cancel
> again with force = false? What happens? Can it cause issues?
>
>> static int block_job_finish_sync(BlockJob *job,
>> @@ -437,7 +438,7 @@ static void block_job_completed_txn_abort(BlockJob *job)
>> * on the caller, so leave it. */
>> QLIST_FOREACH(other_job, &txn->jobs, txn_list) {
>> if (other_job != job) {
>> - block_job_cancel_async(other_job);
>> + block_job_cancel_async(other_job, true);
>
> What's the rationale for deciding that transactional cancellations are
> always force=true?
>
> Granted, this doesn't matter currently because mirror isn't a
> transactional job, but that makes the decision all the more curious.
>
>> }
>> }
>> while (!QLIST_EMPTY(&txn->jobs)) {
>> @@ -542,10 +543,10 @@ void block_job_user_resume(BlockJob *job)
>> }
>> }
>>
>> -void block_job_cancel(BlockJob *job)
>> +void block_job_cancel(BlockJob *job, bool force)
>> {
>> if (block_job_started(job)) {
>> - block_job_cancel_async(job);
>> + block_job_cancel_async(job, force);
>> block_job_enter(job);
>> } else {
>> block_job_completed(job, -ECANCELED);
>> @@ -557,7 +558,7 @@ void block_job_cancel(BlockJob *job)
>> * function pointer casts there. */
>> static void block_job_cancel_err(BlockJob *job, Error **errp)
>> {
>> - block_job_cancel(job);
>> + block_job_cancel(job, false);
>> }
>>
>> int block_job_cancel_sync(BlockJob *job)
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index 15620c9..c8bb414 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -106,7 +106,8 @@ ETEXI
>> .args_type = "force:-f,device:B",
>> .params = "[-f] device",
>> .help = "stop an active background block operation (use -f"
>> - "\n\t\t\t if the operation is currently paused)",
>> + "\n\t\t\t if you want to abort the operation
>> immediately"
>> + "\n\t\t\t instead of keep running until data is in
>> sync )",
>> .cmd = hmp_block_job_cancel,
>> },
>>
>> diff --git a/include/block/blockjob.h b/include/block/blockjob.h
>> index 00403d9..4a96c42 100644
>> --- a/include/block/blockjob.h
>> +++ b/include/block/blockjob.h
>> @@ -63,6 +63,12 @@ typedef struct BlockJob {
>> bool cancelled;
>>
>> /**
>> + * Set to true if the job should be abort immediately without waiting
>> + * for data is in sync.
>> + */
>> + bool force;
>> +
>> + /**
>> * Counter for pause request. If non-zero, the block job is either
>> paused,
>> * or if busy == true will pause itself as soon as possible.
>> */
>> @@ -218,10 +224,11 @@ void block_job_start(BlockJob *job);
>> /**
>> * block_job_cancel:
>> * @job: The job to be canceled.
>> + * @force: Quit a job without waiting data is in sync.
>> *
>> * Asynchronously cancel the specified job.
>> */
>> -void block_job_cancel(BlockJob *job);
>> +void block_job_cancel(BlockJob *job, bool force);
>>
>> /**
>> * block_job_complete:
>> diff --git a/qapi/block-core.json b/qapi/block-core.json
>> index 8225308..7c4dbfe 100644
>> --- a/qapi/block-core.json
>> +++ b/qapi/block-core.json
>> @@ -2098,8 +2098,10 @@
>> # the name of the parameter), but since QEMU 2.7 it can have
>> # other values.
>> #
>> -# @force: whether to allow cancellation of a paused job (default
>> -# false). Since 1.3.
>> +# @force: #optional whether to allow cancellation a job without waiting
>> data is
>> +# in sync, please not that since 2.12 it's semantic is not exactly
>> the
>> +# same as before, from 1.3 to 2.11 it means whether to allow
>> cancellation
>> +# of a paused job (default false). Since 1.3.
>> #
>> # Returns: Nothing on success
>> # If no background operation is active on this device,
>> DeviceNotActive
>> diff --git a/tests/test-blockjob-txn.c b/tests/test-blockjob-txn.c
>> index 3591c96..53daadb 100644
>> --- a/tests/test-blockjob-txn.c
>> +++ b/tests/test-blockjob-txn.c
>> @@ -125,7 +125,7 @@ static void test_single_job(int expected)
>> block_job_start(job);
>>
>> if (expected == -ECANCELED) {
>> - block_job_cancel(job);
>> + block_job_cancel(job, false);
>> }
>>
>> while (result == -EINPROGRESS) {
>> @@ -173,10 +173,10 @@ static void test_pair_jobs(int expected1, int
>> expected2)
>> block_job_txn_unref(txn);
>>
>> if (expected1 == -ECANCELED) {
>> - block_job_cancel(job1);
>> + block_job_cancel(job1, false);
>> }
>> if (expected2 == -ECANCELED) {
>> - block_job_cancel(job2);
>> + block_job_cancel(job2, false);
>> }
>>
>> while (result1 == -EINPROGRESS || result2 == -EINPROGRESS) {
>> @@ -231,7 +231,7 @@ static void test_pair_jobs_fail_cancel_race(void)
>> block_job_start(job1);
>> block_job_start(job2);
>>
>> - block_job_cancel(job1);
>> + block_job_cancel(job1, false);
>>
>> /* Now make job2 finish before the main loop kicks jobs. This simulates
>> * the race between a pending kick and another job completing.
>>
>
> --js
>
This patch also causes an interesting regression in iotest 185:
185 1s ... - output mismatch (see 185.out.bad)
--- /home/bos/jhuston/src/qemu/tests/qemu-iotests/185.out 2017-12-21
16:15:50.879455552 -0500
+++ /home/bos/jhuston/src/qemu/bin/git/tests/qemu-iotests/185.out.bad
2018-01-30 15:38:47.936925014 -0500
@@ -28,16 +28,18 @@
{"return": {}}
{"return": {}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "SHUTDOWN", "data": {"guest": false}}
-{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "BLOCK_JOB_CANCELLED", "data": {"device": "disk", "len":
4194304, "offset": 4194304, "speed": 65536, "type": "commit"}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "BLOCK_JOB_READY", "data": {"device": "disk", "len": 4194304,
"offset": 4194304, "speed": 65536, "type": "commit"}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "BLOCK_JOB_COMPLETED", "data": {"device": "disk", "len":
4194304, "offset": 4194304, "speed": 65536, "type": "commit"}}
=== Start mirror job and exit qemu ===
{"return": {}}
Formatting 'TEST_DIR/t.qcow2.copy', fmt=qcow2 size=67108864
cluster_size=65536 lazy_refcounts=off refcount_bits=16
{"return": {}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "BLOCK_JOB_READY", "data": {"device": "disk", "len": 4194304,
"offset": 4194304, "speed": 65536, "type": "mirror"}}
{"return": {}}
{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "SHUTDOWN", "data": {"guest": false}}
-{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "BLOCK_JOB_CANCELLED", "data": {"device": "disk", "len":
4194304, "offset": 4194304, "speed": 65536, "type": "mirror"}}
+{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP},
"event": "BLOCK_JOB_COMPLETED", "data": {"device": "disk", "len":
4194304, "offset": 4194304, "speed": 65536, "type": "mirror"}}