Messages in this thread Patch in this message | | | From | Justin TerAvest <> | Date | Fri, 11 Mar 2011 08:07:17 -0800 | Subject | Re: [RFC] [PATCH 0/6] Provide cgroup isolation for buffered writes. |
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On Thu, Mar 10, 2011 at 6:47 PM, Vivek Goyal <vgoyal@redhat.com> wrote: > On Wed, Mar 09, 2011 at 10:04:11AM -0800, Justin TerAvest wrote: >> On Tue, Mar 8, 2011 at 2:50 PM, Vivek Goyal <vgoyal@redhat.com> wrote: >> > On Tue, Mar 08, 2011 at 05:43:25PM -0500, Vivek Goyal wrote: >> >> On Tue, Mar 08, 2011 at 01:20:50PM -0800, Justin TerAvest wrote: >> >> > This patchset adds tracking to the page_cgroup structure for which cgroup has >> >> > dirtied a page, and uses that information to provide isolation between >> >> > cgroups performing writeback. >> >> > >> >> >> >> Justin, >> >> >> >> So if somebody is trying to isolate a workload which does bunch of READS >> >> and lots of buffered WRITES, this patchset should help in the sense that >> >> all the heavy WRITES can be put into a separate cgroup of low weight? >> >> >> >> Other application which are primarily doing READS, direct WRITES or little >> >> bit of buffered WRITES should still get good latencies if heavy writer >> >> is isolated in a separate group? >> >> >> >> If yes, then this piece standalone can make sense. And once the other >> >> piece/patches of memory cgroup dirty ratio and cgroup aware buffered >> >> writeout come in, then one will be able to differentiate buffered writes >> >> of different groups. >> > >> > Thinking more about it, currently anyway SYNC preempts the ASYNC. So the >> > question would be will it help me enable get better isolation latencies >> > of READS agains buffered WRITES? >> >> Ah! Sorry, I left out a patch that disables cross-group preemption. >> I'll add that to the patchset and email out v2 soon. > > Well, what I was referring to that even in current code sync preempts > all async in CFQ. So it looks like this patchset will not help get > better latencies in presence of WRITES?
Hi Vivek,
I should have been more clear. I forgot to include a patch that changes the behavior of that preemption. I haven't mailed out v2 yet because I was also writing a change to put the css_id in pc->flags instead of its own field.
The preemption change would look like:
Previously, a sync queue in can preempt an async queue in another cgroup. This changes that behavior to disallow such preemption.
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index ab7a216..0494c0c 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -3390,6 +3390,9 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue if (!cfqq) return false;
+ if (new_cfqq->cfqg != cfqq->cfqg) + return false; + if (cfq_class_idle(new_cfqq)) return false;
@@ -3409,9 +3412,6 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq)) return true;
- if (new_cfqq->cfqg != cfqq->cfqg) - return false;
I will include the test results that show that isolation is also improved between a reader and a buffered writer.
Thanks, Justin
> The only place it can help is that one is looking for service differentation > between two or more buffered write streams. For that we need to fix > upper layers first. > > Vivek >
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