On Mon, Jan 16, 2012 at 10:41 AM, Mulyadi Santosa <mulyadi.santosa@xxxxxxxxx> wrote: > Hi Prateek... > > On Mon, Jan 16, 2012 at 11:48, Prateek Sharma <prateek3.14@xxxxxxxxx> wrote: >> The latencytop output for the process doing the IO (qemu) is below: >> >> Process qemu-system-x86 (6239) Total: 31363.7 msec >> [sleep_on_page] 1966.5 msec 81.4 % >> Waiting for event (select) 5.0 msec 7.8 % >> [kvm_vcpu_block] 5.0 msec 8.5 % >> synchronous write 1.7 msec 0.0 % >> Userspace lock contention 1.5 msec 2.3 % > > Which qemu version do you use now? AFAIK certain new qemu versions > already uses iothreads by default. That should reduce I/O latency... > AFAIK too iothreads is not enabled by default...but for qemu 1.0 above > it's enabled by default. Are you compiling from source? > I am using qemu-kvm 0.15, with KVM. > Regarding the function sleep_on_page(). It's in turn io_schedule(). > And here's the comment above the function declaration of > io_schedule(): > /* > * This task is about to go to sleep on IO. Increment rq->nr_iowait so > * that process accounting knows that this is a task in IO wait state. > */ > > You can confirm it by yourself in: > http://lxr.linux.no/#linux+v3.2.1/kernel/sched.c#L5872 > My initial understanding was that sleep_on_page is 'called' by __lock_page, which is usually called by file_read . So, i assumed that sleep_on_page is for the page-lock contention. My primary confusion is with the interpretation of latencytop output. 2 seconds even for I/O to complete seems awfully long. > Hope it helps.... > > -- > regards, > > Mulyadi Santosa > Freelance Linux trainer and consultant > > blog: the-hydra.blogspot.com > training: mulyaditraining.blogspot.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
