linux-kernel - Re: [git pull] scheduler updates

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]

Message-ID: <20081117225018.GA25619@elte.hu>
Date:	Mon, 17 Nov 2008 23:50:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Venki Pallipadi <venkatesh.pallipadi@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: [git pull] scheduler updates


* Venki Pallipadi <venkatesh.pallipadi@...el.com> wrote:

> Patch being discussed on this thread (commit 0d12cdd) has a 
> regression on one of the test systems here.
> 
> With the patch, I see
> 
> checking TSC synchronization [CPU#0 -> CPU#1]:
> Measured 28 cycles TSC warp between CPUs, turning off TSC clock.
> Marking TSC unstable due to check_tsc_sync_source failed
> 
> Whereas, without the patch syncs pass fine on all CPUs
> 
> checking TSC synchronization [CPU#0 -> CPU#1]: passed.
> 
> Due to this, TSC is marke unstable, when it is not actually unstable.
> This is because syncs in check_tsc_wrap() goes away due to this commit.
> 
> As per the discussion on this thread, correct way to fix this is to add
> explicit syncs as below?

ah. Yes.

Could you please check whether:

> +	rdtsc_barrier();
>  	start = get_cycles();
> +	rdtsc_barrier();
>  	/*
>  	 * The measurement runs for 20 msecs:
>  	 */
> @@ -61,7 +63,9 @@ static __cpuinit void check_tsc_warp(voi
>  		 */
>  		__raw_spin_lock(&sync_lock);
>  		prev = last_tsc;
> +		rdtsc_barrier();
>  		now = get_cycles();
> +		rdtsc_barrier();

adding the barrier just _after_ the get_cycles() call (but not before 
it) does the trick too? That should be enough in this case.

	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/