Messages in this thread | | | Date | Mon, 14 Mar 2011 23:52:36 +0800 | From | "Lina Lu" <> | Subject | Re: Re: Re: blk-throttle.c : When limit is changed, must start anewslice |
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On 2011-03-14 23:18:31, Vivek Goyal wrote: >On Sat, Mar 12, 2011 at 07:33:07PM +0800, Lina Lu wrote: >> On 2011-03-11 03:55:55, Vivek Goyal wrote: >> >On Fri, Mar 11, 2011 at 12:38:18AM +0800, Lina Lu wrote: >> >> [..] >> >> Hi Vivek, >> >> I have test the following patch, but the latency still there. >> >> >> >> I try to find why there are 5~10 seconds latency today. After collect the blktrace, I >> >> think the reason is that throtl_trim_slice() don't aways update the tg->slice_start[rw], >> >> although we call it once dispatch a bio. >> > >> >lina, >> > >> >Trim slice should not even matter now. Upon limit change, this patch >> >should reset the slice and start a new one irrespective of the fact >> >where are. >> > >> >In your traces, do you see limit change message and do you see a new >> >slice starting. >> > >> >I did similar test yesterday on my box and this patch worked. Can you >> >capture some block traces and I can have a look at those. Key thing >> >to look for is limit change message and whether it started a new >> >slice or not. >> > >> >Thanks >> >Vivek >> > >> >> Hi Vivek, >> >> Here is the blktrace and iostat results when I change the limit from 1024000000000000 >> to 1024000. When the limit changed, there is about 3 seconds lantency. >> >> blktrace: >> 253,1 0 0 4.177733270 0 m N throtl / [R] trim slice nr=1 bytes=102400000000000 io=429496729 start=4297788991 end=4297789100 jiffies=4297788992 >> 253,1 0 0 4.187393582 0 m N throtl / [R] extend slice start=4297788991 end=4297789200 jiffies=4297789002 >> 253,1 0 0 4.276120505 0 m N throtl / [R] trim slice nr=1 bytes=102400000000000 io=429496729 start=4297789091 end=4297789200 jiffies=4297789091 >> 253,1 0 0 4.285934091 0 m N throtl / [R] extend slice start=4297789091 end=4297789300 jiffies=4297789101 >> 253,1 1 0 4.348552814 0 m N throtl schedule work. delay=0 jiffies=4297789163 >> 253,1 1 0 4.348571560 0 m N throtl limit changed =1 >> 253,1 0 0 4.349839104 0 m N throtl / [R] extend slice start=4297789091 end=4297793000 jiffies=4297789164 >> 253,1 0 0 4.349844118 0 m N throtl / [R] bio. bdisp=3928064 sz=4096 bps=1024000 iodisp=959 iops=4294967295 queued=0/0 > >Lina, > >Thanks for the traces. > >I think we did call process_limit_change() but we did not start the new >slice. I guess this happened because, we seem to be starting slice only >if group on run tree. Because before limit udpates, most likely group >is not on run tree as limits are very high, hence we missed resetting >the slice. > > hlist_for_each_entry_safe(tg, pos, n, &td->tg_list, tg_node) { > if (throtl_tg_on_rr(tg) && tg->limits_changed) { > throtl_log_tg(td, tg, "limit change rbps=%llu wbps=%llu" > " riops=%u wiops=%u", tg->bps[READ], > tg->bps[WRITE], tg->iops[READ], > tg->iops[WRITE]); >
Do you mean that throtl_tg_on_rr() function returns 0 when the limits are very high?
>Actually many races have been fixed in Jens's block tree. Is it possible to >test origin/for-2.6.39/core branch of Jens's tree with following patch applied >and see if it fixes the issue for you?
I only find 2.6.38 core in gitweb. Do you mean origin/for-2.6.38/core branch? I'll test it as soon as possible and keep you know the result.
>Thanks >Vivek > >--- > block/blk-throttle.c | 25 ++++++++++++++++++++++++- > 1 file changed, 24 insertions(+), 1 deletion(-) > >Index: linux-2.6-block/block/blk-throttle.c >=================================================================== >--- linux-2.6-block.orig/block/blk-throttle.c 2011-03-14 10:27:57.000000000 -0400 >+++ linux-2.6-block/block/blk-throttle.c 2011-03-14 10:30:47.267170956 -0400 >@@ -756,6 +756,15 @@ static void throtl_process_limit_change( > " riops=%u wiops=%u", tg->bps[READ], tg->bps[WRITE], > tg->iops[READ], tg->iops[WRITE]); > >+ /* >+ * Restart the slices for both READ and WRITES. It >+ * might happen that a group's limit are dropped >+ * suddenly and we don't want to account recently >+ * dispatched IO with new low rate >+ */ >+ throtl_start_new_slice(td, tg, 0); >+ throtl_start_new_slice(td, tg, 1); >+ > if (throtl_tg_on_rr(tg)) > tg_update_disptime(td, tg); > } >@@ -821,7 +830,8 @@ throtl_schedule_delayed_work(struct thro > > struct delayed_work *dwork = &td->throtl_work; > >- if (total_nr_queued(td) > 0) { >+ /* schedule work if limits changed even if no bio is queued */ >+ if (total_nr_queued(td) > 0 || td->limits_changed) { > /* > * We might have a work scheduled to be executed in future. > * Cancel that and schedule a new one. >@@ -1002,6 +1012,19 @@ int blk_throtl_bio(struct request_queue > /* Bio is with-in rate limit of group */ > if (tg_may_dispatch(td, tg, bio, NULL)) { > throtl_charge_bio(tg, bio); >+ >+ /* >+ * We need to trim slice even when bios are not being queued >+ * otherwise it might happen that a bio is not queued for >+ * a long time and slice keeps on extending and trim is not >+ * called for a long time. Now if limits are reduced suddenly >+ * we take into account all the IO dispatched so far at new >+ * low rate and * newly queued IO gets a really long dispatch >+ * time. >+ * >+ * So keep on trimming slice even if bio is not queued. >+ */ >+ throtl_trim_slice(td, tg, rw); > goto out; > }
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