On 04/04/2012 09:37 PM, Vivek Goyal wrote: > On Wed, Apr 04, 2012 at 05:35:49AM -0700, Shaohua Li wrote: > > [..] >>>> How iops_weight and switching different than CFQ group scheduling logic? >>>> I think shaohua was talking of using similar logic. What would you do >>>> fundamentally different so that without idling you will get service >>>> differentiation? >>> I am thinking of differentiate different groups with iops, so if there >>> are 3 groups(the weight are 100, 200, 300) we can let them submit 1 io, >>> 2 io and 3 io in a round-robin way. With a intel ssd, every io can be >>> finished within 100us. So the maximum latency for one io is about 600us, >>> still less than 1ms. But with cfq, if all the cgroups are busy, we have >>> to switch between these group in ms which means the maximum latency will >>> be 6ms. It is terrible for some applications since they use ssds now. >> Yes, with iops based scheduling, we do queue switching for every request. >> Doing the same thing between groups is quite straightforward. The only issue >> I found is this will introduce more process context switch, this isn't >> a big issue >> for io bound application, but depends. It cuts latency a lot, which I >> guess is more >> important for web 2.0 application. > > In iops_mode(), expire each cfqq after dispatch of 1 or bunch of requests > and you should get the same behavior (with slice_idle=0 and group_idle=0). > So why write a new scheduler. really? How could we config cfq to work like this? Or you mean we can change the code for it? > > Only thing is that with above, current code will provide iops fairness only > for groups. We should be able to tweak queue scheduling to support iops > fairness also. OK, as I have said in another e-mail another my concern is the complexity. It will make cfq too much complicated. I just checked the source code of shaohua's original patch, fiops scheduler is only ~700 lines, so with cgroup support added it would be ~1000 lines I guess. Currently cfq-iosched.c is around ~4000 lines even after Tejun's cleanup of io context... Thanks Tao > > Anyway, we will end up doing that at some point of time. Supporting two > scheduling algorihtms for queue and groups is not sustainable. There are > already calls to make CFQ hierarchical and in that case both queue and > groups need to be on a single service tree and that means need to follow > same algorithm for scheduling. > > Thanks > Vivek > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
