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Subject: Re: [RFC PATCH v2] posix timers: allocate timer id per task
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: peterz@infradead.org, mingo@redhat.com, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, devel@openvz.org
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Date: Wed, 17 Oct 2012 15:44:26 +0200
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On Wed, 2012-10-17 at 17:18 +0400, Stanislav Kinsbursky wrote:

> +static int hash(struct signal_struct *sig, unsigned int nr)
> +{
> +	int hash = hash_ptr(sig, POSIX_TIMERS_HASH_BITS);
> +	return hash ^ hash_32(nr, POSIX_TIMERS_HASH_BITS);
> +}
> +

This is quite expensive on 64 bit arches. I suggest instead :

return hash_32(hash32_ptr(sig) ^ nr, POSIX_TIMERS_HASH_BITS);