From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Julien Grall <julien.grall@linaro.org>,
Anup Patel <anup.patel@linaro.org>
Cc: Ian Campbell <Ian.Campbell@citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
patches <patches@apm.com>, xen-devel <xen-devel@lists.xen.org>,
"stefano.stabellini" <stefano.stabellini@citrix.com>,
Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Subject: Re: [PATCH] xen/arm: minor improvement in smp_send_call_function_mask()
Date: Thu, 21 Aug 2014 18:22:03 +0100 [thread overview]
Message-ID: <53F62ABB.6080203@citrix.com> (raw)
In-Reply-To: <53F62455.2030906@linaro.org>
On 21/08/14 17:54, Julien Grall wrote:
> Hi Anup,
>
> On 21/08/14 06:04, Anup Patel wrote:
>>> The best alternative would be cpumask_empty.
>>
>> All three cpumask_empty(), cpumask_first(), and cpumask_weight()
>> are O(N) where N is number of bits in cpumask.
>> It really does not make much difference which of these operation
>> is chosen.
They are all O(N), but O() notation hides lesser factors.
cpumask_empty() is slightly cheaper than cpumask_first(), which are both
substantially cheaper than cpumask_weight().
There is no fastpath for calculating the hamming weight of 0, resulting
in a lot of dependent shift/mask operations.
~Andrew
prev parent reply other threads:[~2014-08-21 17:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-19 4:48 [PATCH] xen/arm: minor improvement in smp_send_call_function_mask() Anup Patel
2014-08-19 21:06 ` Julien Grall
2014-08-20 6:14 ` Anup Patel
2014-08-20 15:07 ` Julien Grall
2014-08-21 11:04 ` Anup Patel
2014-08-21 16:54 ` Julien Grall
2014-08-21 17:22 ` Andrew Cooper [this message]
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