On Fri, Oct 09 2009, Wu Fengguang wrote: > On Thu, Oct 08, 2009 at 04:36:09PM +0800, Jens Axboe wrote: > > On Thu, Oct 08 2009, Peter Zijlstra wrote: > > > On Thu, 2009-10-08 at 09:58 +0800, Wu Fengguang wrote: > > > > > > > > > How this runqueue->nr_iowait is handled now ? > > > > > > > > Good question. io_schedule() has an old comment for throttling IO wait: > > > > > > > > * But don't do that if it is a deliberate, throttling IO wait (this task > > > > * has set its backing_dev_info: the queue against which it should throttle) > > > > */ > > > > void __sched io_schedule(void) > > > > > > > > So it looks both Jens' and this patch behaves right in ignoring the > > > > iowait accounting for balance_dirty_pages() :) > > > > > > Well it is a change in behaviour, and I think IOWAIT makes sense when > > > we're blocked due to io throttle.. > > > > > > Hmm? > > > > Yep agree, if we're deliberately waiting on IO, it should count as > > iowait time. > > Then let's revert to the old behavior :) > > For one single cp, it increases iowait from 29% to 56%. > > Before patch: > > ----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system-- > usr sys idl wai hiq siq| read writ| recv send| in out | int csw > 0 4 64 28 0 3| 0 0 | 272k 10M| 0 0 |1854 863 > 0 6 69 23 0 3| 0 0 | 249k 11M| 0 0 |1709 865 > 0 6 64 27 0 4| 0 0 | 235k 10M| 0 0 |1807 788 > 0 4 61 30 0 4| 0 0 | 271k 12M| 0 0 |1910 898 > 0 4 72 21 0 4| 0 0 | 289k 13M| 0 0 |1832 905 > 0 6 58 35 0 2| 0 0 | 252k 11M| 0 0 |1713 900 > 0 4 54 38 0 4| 0 0 | 257k 11M| 0 0 |1777 841 > 0 5 59 30 0 7| 0 0 | 270k 12M| 0 0 |1758 836 > > After patch: > > ----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system-- > usr sys idl wai hiq siq| read writ| recv send| in out | int csw > 0 5 35 57 0 4| 0 0 | 255k 11M| 0 0 |1705 879 > 0 4 38 53 0 4| 0 0 | 326k 14M| 0 0 |1940 980 > 0 3 36 59 0 2| 0 0 | 291k 13M| 0 0 |1970 970 > 0 4 28 66 0 2| 0 0 | 290k 13M| 0 0 |1805 928 > 0 6 38 54 0 3| 0 0 | 230k 10M| 0 0 |1866 842 > 0 5 44 49 0 4| 0 0 | 278k 12M| 0 0 |1808 868 > > Thanks, > Fengguang > --- > writeback: account IO throttling wait as iowait > > It makes sense to do IOWAIT when someone is blocked > due to IO throttle, as suggested by Kame and Peter. > > There is an old comment for not doing IOWAIT on throttle, > however it has been mismatching the code for a long time. > > If we stop accounting IOWAIT for 2.6.32, it could be an > undesirable behavior change. So restore the io_schedule. Thanks, queued up. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
