From: Peter Zijlstra <peterz@infradead•org>
To: Preeti U Murthy <preeti@linux•vnet.ibm.com>
Cc: Michael Neuling <mikey@neuling•org>,
Vincent Guittot <vincent.guittot@linaro•org>,
Mike Galbraith <bitbucket@online•de>,
linuxppc-dev@lists•ozlabs.org,
linux-kernel <linux-kernel@vger•kernel.org>,
Anton Blanchard <anton@samba•org>, Paul Turner <pjt@google•com>,
Ingo Molnar <mingo@kernel•org>
Subject: Re: [PATCH 1/3] sched: Fix nohz_kick_needed to consider the nr_busy of the parent domain's group
Date: Tue, 29 Oct 2013 14:26:29 +0100 [thread overview]
Message-ID: <20131029132629.GC16117@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <526F2BEC.3040207@linux.vnet.ibm.com>
On Tue, Oct 29, 2013 at 09:00:52AM +0530, Preeti U Murthy wrote:
> > Oh nice, that gets rid of the multiple atomics, and it nicely splits
> > this nohz logic into per topology groups -- now if only we could split
> > the rest too :-)
>
> I am sorry, I don't get you here. By the 'rest', do you refer to
> nohz_kick_needed() as below? Or am I missing something?
Nah, the rest of the NOHZ infrastructure. Currently its global state;
there were some patches a few years ago that attempted to make that
per-node state, but that work stalled due to people switching jobs.
> >> + sd = highest_flag_domain(cpu, SD_ASYM_PACKING);
> >> +
> >> + if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
> >> + sched_domain_span(sd)) < cpu))
> >> + goto need_kick_unlock;
> >> +
> >> rcu_read_unlock();
> >> return 0;
> >
> > This again is a bit sad; most archs will not have SD_ASYM_PACKING set at
> > all; this means that they all will do a complete (and pointless) sched
> > domain tree walk here.
>
> There will not be a 'complete' sched domain tree walk right? The
> iteration will break at the first level of the sched domain for those
> archs which do not have SD_ASYM_PACKING set at all.
Ah indeed; I think I got confused due to me modifying
highest_flag_domain() earlier to assume a flag is carried from the
lowest domain upwards.
> But it is true that doing a sched domain tree walk regularly is a bad
> idea, might as well update the domain with SD_ASYM_PACKING flag set once
> and query this domain when required.
>
> I will send out the patch with sd_asym domain introduced rather than the
> above.
Thanks
next prev parent reply other threads:[~2013-10-29 13:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-21 11:44 [PATCH 0/3] sched: Fixes for task placement in SMT threads Vaidyanathan Srinivasan
2013-10-21 11:44 ` [PATCH 1/3] sched: Fix nohz_kick_needed to consider the nr_busy of the parent domain's group Vaidyanathan Srinivasan
2013-10-22 14:35 ` Kamalesh Babulal
2013-10-22 16:40 ` Preeti U Murthy
2013-10-22 22:11 ` Peter Zijlstra
2013-10-23 4:00 ` Preeti U Murthy
2013-10-23 4:21 ` Preeti U Murthy
2013-10-23 9:50 ` Preeti U Murthy
2013-10-23 15:28 ` Vincent Guittot
2013-10-24 8:07 ` Preeti U Murthy
2013-10-28 13:50 ` Peter Zijlstra
2013-10-29 3:30 ` Preeti U Murthy
2013-10-29 13:26 ` Peter Zijlstra [this message]
2013-10-21 11:44 ` [PATCH 2/3] sched: Fix asymmetric scheduling for POWER7 Vaidyanathan Srinivasan
2013-10-21 22:55 ` Michael Neuling
2013-10-22 22:18 ` Peter Zijlstra
2013-10-21 11:45 ` [PATCH 3/3] sched: Aggressive balance in domains whose groups share package resources Vaidyanathan Srinivasan
2013-10-22 22:23 ` Peter Zijlstra
2013-10-24 4:04 ` Preeti U Murthy
2013-10-25 13:19 ` Preeti U Murthy
2013-10-28 15:53 ` Peter Zijlstra
2013-10-29 5:35 ` Preeti U Murthy
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