Hi Stefan, >>By the way, why did you choose 10 milliseconds? That is quite long. >> >>If this function is called once per 10 ms disk I/O operations then we >>lose 50% utilization. 1 ms or less would be reasonable.
>From my tests, 1ms is not enough, It still hanging in guest or qmp queries. 10ms give me optimal balance between bitmap scan speed and guest responsiveness. I don't known if this can be compute automaticaly ? (maybe it's depend of disk lseek speed and cpu speed). ----- Mail original ----- De: "Stefan Hajnoczi" <stefa...@gmail.com> À: "Fam Zheng" <f...@redhat.com> Cc: "Kevin Wolf" <kw...@redhat.com>, "qemu-devel" <qemu-devel@nongnu.org>, qemu-bl...@nongnu.org Envoyé: Jeudi 9 Juillet 2015 14:54:55 Objet: Re: [Qemu-devel] [Qemu-block] [PATCH 1/3] blockjob: Introduce block_job_relax_cpu On Thu, Jul 09, 2015 at 11:47:56AM +0800, Fam Zheng wrote: > block_job_sleep_ns is called by block job coroutines to yield the > execution to VCPU threads and monitor etc. It is pointless to sleep for > 0 or a few nanoseconds, because that equals to a "yield + enter" with no > intermission in between (the timer fires immediately in the same > iteration of event loop), which means other code still doesn't get a > fair share of main loop / BQL. > > Introduce block_job_relax_cpu which will at least for > BLOCK_JOB_RELAX_CPU_NS. Existing block_job_sleep_ns(job, 0) callers can > be replaced by this later. > > Reported-by: Alexandre DERUMIER <aderum...@odiso.com> > Signed-off-by: Fam Zheng <f...@redhat.com> > --- > include/block/blockjob.h | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/include/block/blockjob.h b/include/block/blockjob.h > index 57d8ef1..53ac4f4 100644 > --- a/include/block/blockjob.h > +++ b/include/block/blockjob.h > @@ -157,6 +157,22 @@ void *block_job_create(const BlockJobDriver *driver, > BlockDriverState *bs, > */ > void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns); > > +#define BLOCK_JOB_RELAX_CPU_NS 10000000L By the way, why did you choose 10 milliseconds? That is quite long. If this function is called once per 10 ms disk I/O operations then we lose 50% utilization. 1 ms or less would be reasonable. > + > +/** > + * block_job_relax_cpu: > + * @job: The job that calls the function. > + * > + * Sleep a little to avoid intensive cpu time occupation. Block jobs should > + * call this or block_job_sleep_ns (for more precision, but note that 0 ns > is > + * usually not enought) periodically, otherwise the QMP and VCPU could > starve s/enought/enough/ > + * on CPU and/or BQL. > + */ > +static inline void block_job_relax_cpu(BlockJob *job) coroutine_fn is missing.
