Re: [Qemu-devel] [PATCH v2 11/13] block/mirror: remove block_job_sleep_ns calls

[John Snow]

On 02/07/2018 05:46 PM, Max Reitz wrote:
> Errr.  Are you sure about that?
> 
> Now every mirror job in the qeny process will share this single
> variable.  Was that your intention?
> 

Duh, no.

Thanks for the review, also. I'm currently sidetracked on something
else, so I'll get back to this soon.

Re: [Qemu-devel] [PATCH v2 11/13] block/mirror: remove block_job_sleep_ns calls

[Max Reitz]

On 2018-02-07 23:46, Max Reitz wrote:
> On 2018-01-19 21:58, John Snow wrote:
>> We're attempting to slacken the mirror loop in three different places,
>> but we can combine these three attempts. Combine the early loop call to
>> block_job_pause_point with the two late-loop calls to block_job_sleep_ns.
>>
>> When delay_ns is 0 and it has not been SLICE_TIME since the last yield,
>> block_job_relax is merely a call to block_job_pause_point, so this should
>> be equivalent with the exception that if we have managed to not yield at
>> all in the last SLICE_TIME ns, we will now do so.
>>
>> I am not sure that condition was possible,
>> so this loop should be equivalent.
> 
> Well, to me it even sounds like a positive change if it was a change.
> We want the job to yield after SLICE_TIME ns, after all, and I don't
> think it matters where that happens, exactly.
> 
>>
>> Signed-off-by: John Snow 
>> ---
>>  block/mirror.c | 22 +++---
>>  block/trace-events |  2 +-
>>  2 files changed, 12 insertions(+), 12 deletions(-)
>>
>> diff --git a/block/mirror.c b/block/mirror.c
>> index a0e0044de2..192e03694f 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -761,7 +761,7 @@ static void coroutine_fn mirror_run(void *opaque)
>>  assert(!s->dbi);
>>  s->dbi = bdrv_dirty_iter_new(s->dirty_bitmap);
>>  for (;;) {
>> -uint64_t delay_ns = 0;
>> +static uint64_t delay_ns = 0;
> 
> Errr.  Are you sure about that?
> 
> Now every mirror job in the qeny process will share this single
> variable.  Was that your intention?

("Errr" @myself for "qeny")



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Re: [Qemu-devel] [PATCH v2 11/13] block/mirror: remove block_job_sleep_ns calls

[Max Reitz]

On 2018-01-19 21:58, John Snow wrote:
> We're attempting to slacken the mirror loop in three different places,
> but we can combine these three attempts. Combine the early loop call to
> block_job_pause_point with the two late-loop calls to block_job_sleep_ns.
> 
> When delay_ns is 0 and it has not been SLICE_TIME since the last yield,
> block_job_relax is merely a call to block_job_pause_point, so this should
> be equivalent with the exception that if we have managed to not yield at
> all in the last SLICE_TIME ns, we will now do so.
> 
> I am not sure that condition was possible,
> so this loop should be equivalent.

Well, to me it even sounds like a positive change if it was a change.
We want the job to yield after SLICE_TIME ns, after all, and I don't
think it matters where that happens, exactly.

> 
> Signed-off-by: John Snow 
> ---
>  block/mirror.c | 22 +++---
>  block/trace-events |  2 +-
>  2 files changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index a0e0044de2..192e03694f 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -761,7 +761,7 @@ static void coroutine_fn mirror_run(void *opaque)
>  assert(!s->dbi);
>  s->dbi = bdrv_dirty_iter_new(s->dirty_bitmap);
>  for (;;) {
> -uint64_t delay_ns = 0;
> +static uint64_t delay_ns = 0;

Errr.  Are you sure about that?

Now every mirror job in the qeny process will share this single
variable.  Was that your intention?

>  int64_t cnt, delta;
>  bool should_complete;
>  
> @@ -770,9 +770,16 @@ static void coroutine_fn mirror_run(void *opaque)
>  goto immediate_exit;
>  }
>  
> -block_job_pause_point(>common);
> -
>  cnt = bdrv_get_dirty_count(s->dirty_bitmap);
> +
> +trace_mirror_before_relax(s, cnt, s->synced, delay_ns);
> +if (block_job_relax(>common, delay_ns)) {

See the reply to that patch.

> +if (!s->synced) {
> +goto immediate_exit;
> +}
> +}
> +delay_ns = 0;
> +
>  /* s->common.offset contains the number of bytes already processed so
>   * far, cnt is the number of dirty bytes remaining and
>   * s->bytes_in_flight is the number of bytes currently being
> @@ -849,15 +856,8 @@ 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(>common, delay_ns);
> -if (block_job_is_cancelled(>common)) {
> -break;
> -}
> -} else if (!should_complete) {
> +if (s->synced && !should_complete) {
>  delay_ns = (s->in_flight == 0 && cnt == 0 ? SLICE_TIME : 0);
> -block_job_sleep_ns(>common, delay_ns);
>  }
>  }

Basic idea looks good to me (apart from the static delay_ns), but, well,
block-job-cancel on a busy job still breaks.

Max



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