linux-kernel - Re: [RFC PATCH v2] posix timers: allocate timer id per task

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Date:	Wed, 17 Oct 2012 15:44:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	peterz@...radead.org, mingo@...hat.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: [RFC PATCH v2] posix timers: allocate timer id per task

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);


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