From: Valentin Schneider <email@example.com> To: Steven Sistare <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org Cc: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Re: [PATCH v3 03/10] sched/topology: Provide cfs_overload_cpus bitmap Date: Thu, 6 Dec 2018 17:28:37 +0000 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> Hi Steve, On 06/12/2018 16:40, Steven Sistare wrote: > [...] >> >> Ah yes, that would work. Thing is, I had excluded having the misfit masks >> being in the sd_llc_shareds, since from a logical standpoint they don't >> really belong there. >> >> With asymmetric CPU capacities we kind of disregard the cache landscape > > Sure, but adding awareness of the cache hierarchy can only make it better, > and a per-LLC mask organization can serve both the overloaded and misfit > use cases quite naturally. > [...] >> So in truth I was envisioning separate SD_ASYM_CPUCAPACITY-based >> sparsemasks, which is why I was rambling about SD_ASYM_CPUCAPACITY siblings >> of sd_llc_*()... *But* after I had a go at it, it looked to me like that >> was a lot of duplicated code. > > I would be happy to review your code and make suggestions to reduce duplication, > and happy to continue to discuss clean and optimal handling for misfits. However, > I have a request: can we push my patches across the finish line first? Stealing > for misfits can be its own patch series. Please consider sending your reviewed-by > for the next version of my series. I will send it soon. > Sure, as things stand right now I'm fairly convinced this doesn't harm asymmetric systems. The only thing I would add (ignoring misfits) is that with EAS we would need to gate stealing with something like: !static_branch_unlikely(&sched_energy_present) || READ_ONCE(rq->rd->overutilized) And who "gets" to add this gating (or at least, when must it be added) depends on which patch-set gets in first. [...] >> Sadly I think that doesn't work as well for cfs_overload_cpus since you >> can't split a sparsemask's chunks over several NUMA nodes, so we'd be >> stuck with an allocation on a single node (but we already do that in some >> places, e.g. for nohz.idle_cpus_mask, so... Is it that bad?). > > It can be bad for high memory bandwidth workloads, as the sparsemasks will > be displaced from cache and we incur remote memory latencies on next access. > Aye, I just caught up with the LPC videos and was about to reply here to say that, all things considered, it's probably not such a good idea... > - Steve >
next prev parent reply other threads:[~2018-12-06 17:28 UTC|newest] Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-11-09 12:50 [PATCH v3 00/10] steal tasks to improve CPU utilization Steve Sistare 2018-11-09 12:50 ` [PATCH v3 01/10] sched: Provide sparsemask, a reduced contention bitmap Steve Sistare 2018-11-27 15:16 ` Steven Sistare 2018-11-28 1:19 ` Omar Sandoval 2018-12-06 16:07 ` Steven Sistare 2018-12-06 18:19 ` Omar Sandoval 2018-11-09 12:50 ` [PATCH v3 02/10] sched/topology: Provide hooks to allocate data shared per LLC Steve Sistare 2018-11-09 12:50 ` [PATCH v3 03/10] sched/topology: Provide cfs_overload_cpus bitmap Steve Sistare 2018-11-09 17:38 ` Valentin Schneider 2018-11-19 17:32 ` Steven Sistare 2018-11-20 12:52 ` Valentin Schneider 2018-11-12 16:42 ` Valentin Schneider 2018-11-19 17:33 ` Steven Sistare 2018-11-20 12:42 ` Valentin Schneider 2018-11-26 19:06 ` Steven Sistare 2018-12-03 16:56 ` Valentin Schneider 2018-12-06 16:40 ` Steven Sistare 2018-12-06 17:28 ` Valentin Schneider [this message] 2018-11-09 12:50 ` [PATCH v3 04/10] sched/fair: Dynamically update cfs_overload_cpus Steve Sistare 2018-11-09 12:50 ` [PATCH v3 05/10] sched/fair: Hoist idle_stamp up from idle_balance Steve Sistare 2018-11-09 19:07 ` Valentin Schneider 2018-11-19 17:31 ` Steven Sistare 2018-11-20 10:24 ` Valentin Schneider 2018-11-09 12:50 ` [PATCH v3 06/10] sched/fair: Generalize the detach_task interface Steve Sistare 2018-11-09 12:50 ` [PATCH v3 07/10] sched/fair: Provide can_migrate_task_llc Steve Sistare 2018-11-09 12:50 ` [PATCH v3 08/10] sched/fair: Steal work from an overloaded CPU when CPU goes idle Steve Sistare 2018-11-09 12:50 ` [PATCH v3 09/10] sched/fair: disable stealing if too many NUMA nodes Steve Sistare 2018-11-09 12:50 ` [PATCH v3 10/10] sched/fair: Provide idle search schedstats Steve Sistare 2018-11-10 17:08 ` kbuild test robot 2018-11-09 15:02 ` hackbench run scripts Steven Sistare
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