Hello, Zlatko. Sorry about the delay. Your message was in my spam folder. The attachment seems to have confused the filter.
On Sat, Nov 17, 2012 at 02:01:29PM +0100, Zlatko Calusic wrote: > This week I spent some hours tracking a regression in 3.7 kernel > that was producing high context switch rate on one of my machines. I > carefully bisected between 3.6 and 3.7-rc1 and eventually found this > commit a culprit: > > commit e7c2f967445dd2041f0f8e3179cca22bb8bb7f79 > Author: Tejun Heo <[email protected]> > Date: Tue Aug 21 13:18:24 2012 -0700 > > workqueue: use mod_delayed_work() instead of __cancel + queue ... > > Then I carefully reverted chunk by chunk to find out what exact > change is responsible for the regression. You can find it attached > as wq.patch (to preserve whitespace). Very simple modification with > wildly different behavior on only one of my machines, weird. I'm > also attaching ctxt/s graph that shows the impact nicely. I'll > gladly provide any additional info that could help you resolve this. > > Please Cc: on reply (not subscribed to lkml). > > Regards, > -- > Zlatko > diff --git a/block/blk-core.c b/block/blk-core.c > index 4b4dbdf..4b8b606 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -319,10 +319,8 @@ EXPORT_SYMBOL(__blk_run_queue); > */ > void blk_run_queue_async(struct request_queue *q) > { > - if (likely(!blk_queue_stopped(q))) { > - __cancel_delayed_work(&q->delay_work); > - queue_delayed_work(kblockd_workqueue, &q->delay_work, 0); > - } > + if (likely(!blk_queue_stopped(q))) > + mod_delayed_work(kblockd_workqueue, &q->delay_work, 0); > } > EXPORT_SYMBOL(blk_run_queue_async); That's intersting. Is there anything else noticeably different than the ctxsw counts? e.g. CPU usage, IO throughput / latency, etc... Also, can you please post the kernel boot log from the machine? I assume that the issue is readily reproducible? Are you up for trying some debug patches? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
