[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20120822094153.GA25894@gmail.com>
Date: Wed, 22 Aug 2012 11:41:53 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Rusty Russell <rusty@...tcorp.com.au>
Cc: Suresh Siddha <suresh.b.siddha@...el.com>, x86@...nel.org,
LKML <linux-kernel@...r.kernel.org>,
Paul McKenney <paul.mckenney@...ibm.com>
Subject: Re: [PATCH v2] x86: don't ever patch back to UP if we unplug cpus.
* Rusty Russell <rusty@...tcorp.com.au> wrote:
> We still patch SMP instructions to UP variants if we boot with a
> single CPU, but not at any other time. In particular, not if we
> unplug CPUs to return to a single cpu.
>
> Paul McKenney points out:
>
> mean offline overhead is 6251/48=130.2 milliseconds.
>
> If I remove the alternatives_smp_switch() from the offline
> path [...] the mean offline overhead is 550/42=13.1 milliseconds
>
> Basically, we're never going to get those 120ms back, and the code is
> pretty messy.
>
> We get rid of:
> 1) The "smp-alt-once" boot option. It's actually "smp-alt-boot", the
> documentation is wrong. It's now the default.
> 2) The skip_smp_alternatives flag used by suspend.
> 3) arch_disable_nonboot_cpus_begin() and arch_disable_nonboot_cpus_end()
> which were only used to set this one flag.
>
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> ---
> Documentation/kernel-parameters.txt | 3 -
> arch/x86/include/asm/alternative.h | 4 -
> arch/x86/kernel/alternative.c | 104 +++++++-----------------------------
> arch/x86/kernel/smpboot.c | 20 ------
> kernel/cpu.c | 11 ---
> 5 files changed, 27 insertions(+), 115 deletions(-)
and this version breaks the build on allyesconfig-x86-64:
arch/x86/xen/smp.c:380:3: error: implicit declaration of function ‘alternatives_smp_switch’ [-Werror=implicit-function-declaration]
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists