linux-kernel - Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning

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:	Tue, 15 Sep 2015 11:32:14 -0400
From:	Waiman Long <waiman.long@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning

On 09/15/2015 04:38 AM, Peter Zijlstra wrote:
> On Mon, Sep 14, 2015 at 03:37:32PM -0400, Waiman Long wrote:
>> BTW, the queue head vCPU at pv_wait_head_and_lock() doesn't wait early, it
>> will spin the full threshold as there is no way for it to figure out if the
>> lock holder is running or not.
> We can know its cpu id, right? Surely we should then be able to figure
> out if its active or not, I'm thinking the KVM/Xen know these things
> somewhere.

We can make a guess of the lock holder cpu id by peeking at previous MCS 
node. However, if the current lock holder got the lock without entering 
the queue or it got the lock by stealing, we won't have information of 
what CPU it is.

Cheers,
Longman
--
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/