From: Peter Zijlstra <peterz@infradead•org>
To: Torsten Duwe <duwe@lst•de>
Cc: Tom Musta <tommusta@gmail•com>,
linux-kernel@vger•kernel.org, Paul Mackerras <paulus@samba•org>,
Anton Blanchard <anton@samba•org>,
Scott Wood <scottwood@freescale•com>,
"Paul E. McKenney" <paulmck@linux•vnet.ibm.com>,
linuxppc-dev@lists•ozlabs.org, Ingo Molnar <mingo@kernel•org>
Subject: Re: [PATCH v2] powerpc ticket locks
Date: Mon, 10 Feb 2014 18:53:25 +0100 [thread overview]
Message-ID: <20140210175325.GA27965@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140210155217.GF2107@lst.de>
On Mon, Feb 10, 2014 at 04:52:17PM +0100, Torsten Duwe wrote:
> Opinions, anyone?
Since the holder thing is a performance thing, not a correctness thing;
one thing you could do is something like:
static const int OWNER_HASH_SIZE = CONFIG_NR_CPUS * 4;
static const int OWNER_HASH_BITS = ilog2(OWNER_HASH_SIZE);
u16 lock_owner_array[OWNER_HASH_SIZE] = { 0, };
void set_owner(struct arch_spinlock_t *lock, int owner)
{
int hash = hash_ptr(lock, OWNER_HASH_BITS);
lock_owner_array[hash] = owner;
}
void yield_to_owner(struct arch_spinlock_t *lock)
{
int hash = hash_ptr(lock, OWNER_HASH_BITS);
int owner = lock_owner_array[hash];
yield_to_cpu(owner);
}
And call set_owner() after the ticket lock is acquired, and don't bother
clearing it again; a new acquire will overwrite, a collision we have to
live with.
It should on average get you the right yield and does away with having
to track the owner field in place.
It does however get you an extra cacheline miss on acquire :/
One could consider patching it out when you know your kernel is not
running on an overloaded partition.
next prev parent reply other threads:[~2014-02-10 17:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-07 16:58 [PATCH v2] powerpc ticket locks Torsten Duwe
2014-02-07 17:12 ` Peter Zijlstra
2014-02-07 17:55 ` Torsten Duwe
2014-02-10 3:10 ` Benjamin Herrenschmidt
2014-02-10 15:52 ` Torsten Duwe
2014-02-10 17:53 ` Peter Zijlstra [this message]
2014-02-11 2:44 ` Benjamin Herrenschmidt
2014-02-11 2:56 ` Al Viro
2014-02-11 3:38 ` Benjamin Herrenschmidt
2014-02-11 9:53 ` Raghavendra KT
2014-02-11 10:40 ` Torsten Duwe
2014-02-11 18:30 ` Scott Wood
2014-02-11 19:34 ` Benjamin Herrenschmidt
2014-02-11 9:39 ` Raghavendra KT
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