From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Travis <travis@sgi.com>, Ingo Molnar <mingo@elte.hu>,
davej@codemonkey.org.uk, David Miller <davem@davemloft.net>,
Eric Dumazet <dada1@cosmosbay.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Jack Steiner <steiner@sgi.com>,
Jeremy Fitzhardinge <jeremy@goop.org>, Jes Sorensen <jes@sgi.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, Gautham R Shenoy <ego@in.ibm.com>
Subject: Re: [RFC 07/13] sched: Reduce stack size requirements in kernel/sched.c
Date: Sun, 07 Sep 2008 22:28:01 +0200 [thread overview]
Message-ID: <1220819281.8687.100.camel@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20080907040009.611ac986.akpm@linux-foundation.org>
On Sun, 2008-09-07 at 04:00 -0700, Andrew Morton wrote:
> make cpu_hotplug.refcount an atomic_t.
That might actually be a worthwhile idea, but it will not make
get_online_cpus() atomic. The whole point of get_online_cpus() is to
serialize against actual hotplug operations, so it will have to sleep at
some point.
Now, turning cpu_hotplug.refcount into an atomic_t might be worthwhile
because it will reduce the amount of atomic operations in its fastpath
from 2 to 1.
You'd have to make recount==1 the stable situation and use
atomic_inc_unless() and atomic_dec_and_test() in get_online_cpus() and
put_online_cpus() resp. that way !refcount can signify a hotplug
operation and we'd fall back into the slow paths.
next prev parent reply other threads:[~2008-09-07 20:31 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-06 23:50 [RFC 00/13] smp: reduce stack requirements for genapic send_IPI_mask functions Mike Travis
2008-09-06 23:50 ` [RFC 01/13] smp: modify send_IPI_mask interface to accept cpumask_t pointers Mike Travis
2008-09-06 23:50 ` [RFC 02/13] cpumask: add for_each_online_cpu_mask_nr function Mike Travis
2008-09-06 23:50 ` [RFC 03/13] xen: use new " Mike Travis
2008-09-06 23:50 ` [RFC 04/13] cpumask: add cpumask_ptr operations Mike Travis
2008-09-06 23:50 ` [RFC 05/13] cpumask: add get_cpumask_var debug operations Mike Travis
2008-09-06 23:50 ` [RFC 06/13] genapic: use get_cpumask_var operations for allbutself cpumask_ts Mike Travis
2008-09-06 23:50 ` [RFC 07/13] sched: Reduce stack size requirements in kernel/sched.c Mike Travis
2008-09-07 10:24 ` Peter Zijlstra
2008-09-07 11:00 ` Andrew Morton
2008-09-07 13:05 ` Peter Zijlstra
2008-09-08 14:56 ` Mike Travis
2008-09-07 20:28 ` Peter Zijlstra [this message]
2008-09-08 14:54 ` Mike Travis
2008-09-08 15:05 ` Peter Zijlstra
2008-09-08 18:38 ` Ingo Molnar
2008-09-10 22:47 ` [RFC] CPUMASK: proposal for replacing cpumask_t Mike Travis
2008-09-10 22:53 ` Andi Kleen
2008-09-10 23:33 ` Mike Travis
2008-09-11 5:21 ` Andi Kleen
2008-09-11 9:00 ` Peter Zijlstra
2008-09-11 15:04 ` Mike Travis
2008-09-12 4:55 ` Rusty Russell
2008-09-12 14:28 ` Mike Travis
2008-09-12 22:02 ` Rusty Russell
2008-09-12 22:50 ` Mike Travis
2008-09-12 22:58 ` H. Peter Anvin
2008-09-06 23:50 ` [RFC 08/13] cpufreq: Reduce stack size requirements in acpi-cpufreq.c Mike Travis
2008-09-06 23:50 ` [RFC 09/13] genapic: reduce stack pressuge in io_apic.c step 1 temp cpumask_ts Mike Travis
2008-09-08 11:01 ` Andi Kleen
2008-09-08 16:03 ` Mike Travis
2008-09-06 23:50 ` [RFC 10/13] genapic: reduce stack pressuge in io_apic.c step 2 internal abi Mike Travis
2008-09-06 23:50 ` [RFC 11/13] genapic: reduce stack pressuge in io_apic.c step 3 target_cpus Mike Travis
2008-09-07 7:55 ` Bert Wesarg
2008-09-07 9:13 ` Ingo Molnar
2008-09-08 15:01 ` Mike Travis
2008-09-08 15:29 ` Mike Travis
2008-09-06 23:50 ` [RFC 12/13] genapic: reduce stack pressuge in io_apic.c step 4 vector allocation Mike Travis
2008-09-06 23:50 ` [RFC 13/13] genapic: reduce stack pressuge in io_apic.c step 5 cpu_mask_to_apicid Mike Travis
2008-09-07 7:36 ` [RFC 00/13] smp: reduce stack requirements for genapic send_IPI_mask functions Ingo Molnar
2008-09-08 15:17 ` Mike Travis
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