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 + +/** + * 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 + * on CPU and/or BQL. + */ +static inline void block_job_relax_cpu(BlockJob *job) +{ + return block_job_sleep_ns(job, QEMU_CLOCK_REALTIME, BLOCK_JOB_RELAX_CPU_NS); +} + /** * block_job_yield: * @job: The job that calls the function. -- 2.4.3