On 6/12/19 11:02 PM, Greg Kroah-Hartman wrote: > On Wed, Jun 12, 2019 at 12:36:53PM -0700, Srivatsa S. Bhat wrote: >> >> [ Adding Greg to CC ] >> >> On 6/12/19 6:04 AM, Jan Kara wrote: >>> On Tue 11-06-19 15:34:48, Srivatsa S. Bhat wrote: >>>> On 6/2/19 12:04 AM, Srivatsa S. Bhat wrote: >>>>> On 5/30/19 3:45 AM, Paolo Valente wrote: >>>>>> >>>> [...] >>>>>> At any rate, since you pointed out that you are interested in >>>>>> out-of-the-box performance, let me complete the context: in case >>>>>> low_latency is left set, one gets, in return for this 12% loss, >>>>>> a) at least 1000% higher responsiveness, e.g., 1000% lower start-up >>>>>> times of applications under load [1]; >>>>>> b) 500-1000% higher throughput in multi-client server workloads, as I >>>>>> already pointed out [2]. >>>>>> >>>>> >>>>> I'm very happy that you could solve the problem without having to >>>>> compromise on any of the performance characteristics/features of BFQ! >>>>> >>>>> >>>>>> I'm going to prepare complete patches. In addition, if ok for you, >>>>>> I'll report these results on the bug you created. Then I guess we can >>>>>> close it. >>>>>> >>>>> >>>>> Sounds great! >>>>> >>>> >>>> Hi Paolo, >>>> >>>> Hope you are doing great! >>>> >>>> I was wondering if you got a chance to post these patches to LKML for >>>> review and inclusion... (No hurry, of course!) >>>> >>>> Also, since your fixes address the performance issues in BFQ, do you >>>> have any thoughts on whether they can be adapted to CFQ as well, to >>>> benefit the older stable kernels that still support CFQ? >>> >>> Since CFQ doesn't exist in current upstream kernel anymore, I seriously >>> doubt you'll be able to get any performance improvements for it in the >>> stable kernels... >>> >> >> I suspected as much, but that seems unfortunate though. The latest LTS >> kernel is based on 4.19, which still supports CFQ. It would have been >> great to have a process to address significant issues on older >> kernels too. >> >> Greg, do you have any thoughts on this? The context is that both CFQ >> and BFQ I/O schedulers have issues that cause I/O throughput to suffer >> upto 10x - 30x on certain workloads and system configurations, as >> reported in [1]. >> >> In this thread, Paolo posted patches to fix BFQ performance on >> mainline. However CFQ suffers from the same performance collapse, but >> CFQ was removed from the kernel in v5.0. So obviously the usual stable >> backporting path won't work here for several reasons: >> >> 1. There won't be a mainline commit to backport from, as CFQ no >> longer exists in mainline. >> >> 2. This is not a security/stability fix, and is likely to involve >> invasive changes. >> >> I was wondering if there was a way to address the performance issues >> in CFQ in the older stable kernels (including the latest LTS 4.19), >> despite the above constraints, since the performance drop is much too >> significant. I guess not, but thought I'd ask :-) > > If someone cares about something like this, then I strongly just > recommend they move to the latest kernel version. There should not be > anything stoping them from doing that, right? Nothing "forces" anyone > to be on the 4.19.y release, especially when it really starts to show > its age. > > Don't ever treat the LTS releases as "the only thing someone can run, so > we must backport huge things to it!" Just use 5.1, and then move to 5.2 > when it is out and so on. That's always the preferred way, you always > get better support, faster kernels, newer features, better hardware > support, and most importantly, more bugfixes. > Thank you for the clarification! Regards, Srivatsa VMware Photon OS
