linux-kernel - Re: [PATCH] Do not force shutdown/reboot to boot cpu.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 10 Apr 2013 18:59:34 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Russ Anderson <rja@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Robin Holt <holt@....com>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] Do not force shutdown/reboot to boot cpu.


* Russ Anderson <rja@....com> wrote:

> Yes, I have a test patch that replaces for_each_online_cpu(cpu) with a cpu 
> bitmask in disable_nonboot_cpus().  The lower level routines already take a 
> bitmask.  It allows __stop_machine() to be called just once.  That change 
> reduces shutdown time on a 1024 cpu machine from 16 minutes 4 minutes.  
> Significant improvement, but not good enough.
> 
> The next significant bottleneck is __cpu_notify().  Tried creating worker 
> threads to parallelize the shutdown, but the problem is __cpu_notify() is not 
> thread safe.  Putting a lock around it caused all the worker threads to fight 
> over the lock.

4 minutes bootup is 240 seconds, with 1024 CPUs that's about 240 msecs per CPU.

That sounds a lot, given that unlike bootup there's not much real work to be done 
during shutdown - we don't initialize anything, etc.

Maybe much of those 240 msecs are spent in some stupid udelay loop or so, which 
could be made parallel?

Would it be possible to create a 'reboot but stop at the end and reactivate all 
CPUs again' reboot flag, so that it can all be NMI-profiled, to see where the true 
bottleneck is? A naked disable_nonboot_cpus() call in essence.

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/