linux-kernel - Re: [RFC] NUMA futex hashing

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 for Android: free password hash cracker in your pocket

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

Date:	Tue, 8 Aug 2006 18:59:04 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Ulrich Drepper <drepper@...il.com>, Andi Kleen <ak@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] NUMA futex hashing

On Tuesday 08 August 2006 18:49, Eric Dumazet wrote:
> On Tuesday 08 August 2006 18:34, Nick Piggin wrote:
> > Eric Dumazet wrote:
> > > We certainly can. But if you insist of using mmap sem at all, then we
> > > have a problem.
> > >
> > > rbtree would not reduce cacheline bouncing, so :
> > >
> > > We could use a hashtable (allocated on demand) of size N, N depending
> > > on NR_CPUS for example. each chain protected by a private spinlock. If
> > > N is well chosen, we might reduce lock cacheline bouncing. (different
> > > threads fighting on different private futexes would have a good chance
> > > to get different cachelines in this hashtable)
> >
> > See other mail. We already have a hash table ;)
>
> Yes but still you want at FUTEX_WAIT time to tell the kernel the futex is
> private to this process.
>
> Giving the same info at FUTEX_WAKE time could avoid the kernel to make the
> second pass (using only a private futex lookup), avoiding again the
> mmap_sem touch in case no threads are waiting anymore on this futex.

After looking at kernel/futex.c, I realize we also can avoid the atomic ops 
(and another cacheline bouncing) done in get_key_refs()/drop_key_refs(), 
touching the inode i_count or mm_count refcounter)

Eric
-
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/