From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: zhe.he@windriver.com, acme@kernel.org, ak@linux.intel.com,
alexander.shishkin@linux.intel.com, bp@alien8.de, hpa@zytor.com,
jolsa@kernel.org, jolsa@redhat.com, kan.liang@linux.intel.com,
mingo@redhat.com, namhyung@kernel.org, tglx@linutronix.de,
x86@kernel.org, linux-kernel@vger.kernel.org,
linux-rt-users@vger.kernel.org
Subject: Re: [PATCH] perf/x86/intel: Avoid unnecessary reallocations of memory allocated in cpu hotplug prepare state
Date: Tue, 18 Dec 2018 13:34:22 +0100 [thread overview]
Message-ID: <20181218123421.GI15430@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20181218114708.p6fpz447brob4kzz@linutronix.de>
On Tue, Dec 18, 2018 at 12:47:08PM +0100, Sebastian Andrzej Siewior wrote:
> On 2018-12-18 12:37:00 [+0100], Peter Zijlstra wrote:
> > On Tue, Dec 18, 2018 at 12:31:19PM +0100, Peter Zijlstra wrote:
> > > On Tue, Dec 18, 2018 at 12:16:37PM +0100, Sebastian Andrzej Siewior wrote:
> > > > On 2018-12-18 12:02:09 [+0100], Peter Zijlstra wrote:
> > > > > On Tue, Dec 18, 2018 at 06:30:33PM +0800, zhe.he@windriver.com wrote:
> > > > > > Besides, in preempt-rt full mode, the freeing can happen in atomic context and
> > > > > > thus cause the following BUG.
> > > > >
> > > > > Hurm, I though we fixed all those long ago..
> > > > >
> > > > > And no, the patch is horrible; that's what we have things like
> > > > > x86_pmu::cpu_dead() for.
> > > >
> > > > ehm, you say we keep memory allocation +free on CPU up/down?
> > >
> > > Sure, why not?
>
> It does not seem to be useful to allocate & free memory which you need
> anyway. So you could avoid the refcnt for instance.
It makes the code simpler and hotplug is not what you'd call a fast path
anyway.
> Also I doubt the memory will remain unallocated for a longer period of
> time (like you would remove the CPU for good and not boot it again a
> minute later).
SMT disable comes to mind...
> *Maybe* it is different in cloud environment where you attach vcpus
> depending on guest load at runtime but still…
And that..
next prev parent reply other threads:[~2018-12-18 12:34 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-18 10:30 [PATCH] perf/x86/intel: Avoid unnecessary reallocations of memory allocated in cpu hotplug prepare state zhe.he
2018-12-18 11:02 ` Peter Zijlstra
2018-12-18 11:16 ` Sebastian Andrzej Siewior
2018-12-18 11:31 ` Peter Zijlstra
2018-12-18 11:37 ` Peter Zijlstra
2018-12-18 11:47 ` Sebastian Andrzej Siewior
2018-12-18 12:34 ` Peter Zijlstra [this message]
2018-12-18 12:45 ` He Zhe
2018-12-18 13:59 ` Sebastian Andrzej Siewior
2018-12-19 16:53 ` [PATCH] perf/x86/intel: Delay memory deallocation until x86_pmu_dead_cpu() Sebastian Andrzej Siewior
2018-12-18 11:25 ` [PATCH] perf/x86/intel: Avoid unnecessary reallocations of memory allocated in cpu hotplug prepare state Thomas Gleixner
2018-12-18 11:38 ` Peter Zijlstra
2018-12-18 11:14 ` Sebastian Andrzej Siewior
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