From: Oleg Nesterov <oleg@redhat.com>
To: Gautham R Shenoy <ego@in.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>,
linux-kernel@vger.kernel.org, travis@sgi.com,
Ingo Molnar <mingo@elte.hu>,
Srivatsa Vaddagiri <vatsa@in.ibm.com>
Subject: Re: [PATCH 1/7] work_on_cpu: helper for doing task on a CPU.
Date: Fri, 24 Oct 2008 15:25:09 +0200 [thread overview]
Message-ID: <20081024132509.GB17708@redhat.com> (raw)
In-Reply-To: <20081024114018.GA24080@in.ibm.com>
On 10/24, Gautham R Shenoy wrote:
>
> Having a rule that we shouldn't use work_on_cpu() in cpu-hotplug path
> is a good thing. But maintaining it can be difficult.
>
> We've seen that in the past with the cpucontrol mutex.
> We had clear rules that functions which get called in
> cpu-hotplug callback paths, shouldn't take this mutex. But with
> functions that were called in the cpu-hotplug notifier
> path as well as normal paths, it created a whole locking mess,
> and took quite some time to fix.
>
> Similarly, right now, we can have a BUG_ON() which notifies us whenever
> someone ends up calling a function that invokes work_on_cpu() from the
> CPU-Hotplug callpath. But we will fix it only when the BUG_ON() is hit.
>
> On the other hand, if we have a mechanism that's guaranteed to work
> irrespective of the callpaths, why not use that ?
If we add another wq for work_on_cpu(), then we add another hard-to-maintain
rule: get_online_cpus() must not be used by any work which can be queued
on that wq. And, yet another per-cpu thread...
Personally I don't even think we need a BUG_ON() in work_on_cpu(), because
I don't think cpu-hotplug path is so special.
Not that I have a strong opinion though.
Oleg.
next prev parent reply other threads:[~2008-10-24 13:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-23 16:55 [PATCH 1/7] work_on_cpu: helper for doing task on a CPU Rusty Russell
2008-10-23 7:22 ` Gautham R Shenoy
2008-10-23 9:40 ` Oleg Nesterov
2008-10-23 14:36 ` Gautham R Shenoy
2008-10-23 16:35 ` Oleg Nesterov
2008-10-23 17:02 ` do_boot_cpu can deadlock? Oleg Nesterov
2008-10-23 18:21 ` Gautham R Shenoy
2008-10-23 18:49 ` Cyrill Gorcunov
2008-10-24 9:33 ` Oleg Nesterov
2008-10-24 9:53 ` Gautham R Shenoy
2008-10-24 10:51 ` Oleg Nesterov
2008-10-24 3:04 ` [PATCH 1/7] work_on_cpu: helper for doing task on a CPU Rusty Russell
2008-10-24 7:21 ` Gautham R Shenoy
2008-10-24 10:29 ` Oleg Nesterov
2008-10-24 11:18 ` Rusty Russell
2008-10-24 11:40 ` Gautham R Shenoy
2008-10-24 13:25 ` Oleg Nesterov [this message]
2008-10-24 13:41 ` Gautham R Shenoy
2008-10-24 14:23 ` Oleg Nesterov
2008-10-23 15:10 ` Rusty Russell
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