linux-kernel - Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather than rcu

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: <48B2D3BE.40101@linux-foundation.org>
Date:	Mon, 25 Aug 2008 10:46:06 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	paulmck@...ux.vnet.ibm.com, Pekka Enberg <penberg@...helsinki.fi>,
	Ingo Molnar <mingo@...e.hu>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andi Kleen <andi@...stfloor.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather	than
 rcu

Peter Zijlstra wrote:
>
> If we combine these two cases, and flip the counter as soon as we've
> enqueued one callback, unless we're already waiting for a grace period
> to end - which gives us a longer window to collect callbacks.
> 
> And then the rcu_read_unlock() can do:
> 
>   if (dec_and_zero(my_counter) && my_index == dying)
>     raise_softirq(RCU)
> 
> to fire off the callback stuff.
> 
> /me ponders - there must be something wrong with that...
> 
> Aaah, yes, the dec_and_zero is non trivial due to the fact that its a
> distributed counter. Bugger..

Then lets make it per cpu. If we get the cpu ops in then dec_and_zero would be
very cheap.


--
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/