From: David Vrabel <david.vrabel@citrix.com>
To: Julien Grall <julien.grall.oss@gmail.com>,
Jan Beulich <JBeulich@suse.com>,
Julien Grall <julien.grall@citrix.com>
Cc: xen-devel@lists.xenproject.org,
Ian Campbell <ian.campbell@citrix.com>,
Keir Fraser <keir@xen.org>,
David Vrabel <david.vrabel@citrix.com>, Tim Deegan <tim@xen.org>
Subject: Re: [PATCHv2 5/5] evtchn: pad struct evtchn to 64 bytes
Date: Tue, 16 Jun 2015 14:13:09 +0100 [thread overview]
Message-ID: <558020E5.7050707@citrix.com> (raw)
In-Reply-To: <55801D49.3030508@gmail.com>
On 16/06/15 13:57, Julien Grall wrote:
> On 16/06/15 12:59, Jan Beulich wrote:
>>>>> On 16.06.15 at 13:14, <julien.grall@citrix.com> wrote:
>>> On 15/06/2015 16:48, David Vrabel wrote:
>>>> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
>>>> index 44ea92d..a0ff9d2 100644
>>>> --- a/xen/include/xen/sched.h
>>>> +++ b/xen/include/xen/sched.h
>>>> @@ -129,7 +129,7 @@ struct evtchn
>>>> #endif
>>>> } ssid;
>>>> #endif
>>>> -};
>>>> +} __attribute__((aligned(64)));
>>>
>>> Why don't you use __cacheline_aligned?
>>
>> That would double the size on x86, for little or no benefit.
>
> Well, the cache line size is not necessarily 64 bytes on every
> architecture. In the case of ARM, the cache line depends on the
> processor version.
>
> __cacheline_aligned is the only way to ensure that the cache line is not
> shared on ARM.
>
> AFAIU, the goal of this patch is to avoid sharing the cache line. If
> not, the commit message is misleading because it claims that a cache
> line is always 64 bytes...
We want to avoid sharing the cache line where we can do so for no
additional memory cost.
David
next prev parent reply other threads:[~2015-06-16 13:13 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-15 15:48 [PATCHv2 0/5] evtchn: Improve scalebility David Vrabel
2015-06-15 15:48 ` [PATCHv2 1/5] evtchn: factor out freeing an event channel David Vrabel
2015-06-15 15:48 ` [PATCHv2 2/5] evtchn: simplify port_is_valid() David Vrabel
2015-06-15 15:57 ` Ian Campbell
2015-06-15 15:59 ` David Vrabel
2015-06-15 16:09 ` Ian Campbell
2015-06-15 15:48 ` [PATCHv2 3/5] evtchn: use a per-event channel lock for sending events David Vrabel
2015-06-16 9:18 ` Jan Beulich
2015-06-16 9:34 ` David Vrabel
2015-06-16 9:51 ` Jan Beulich
2015-06-16 9:57 ` David Vrabel
2015-06-16 15:19 ` David Vrabel
2015-06-16 15:58 ` David Vrabel
2015-06-16 16:19 ` Jan Beulich
2015-06-16 16:39 ` David Vrabel
2015-06-17 7:05 ` Jan Beulich
2015-06-16 16:06 ` Jan Beulich
2015-06-15 15:48 ` [PATCHv2 4/5] evtchn: remove the locking when unmasking an event channel David Vrabel
2015-06-16 9:19 ` Jan Beulich
2015-06-16 9:40 ` David Vrabel
2015-06-15 15:48 ` [PATCHv2 5/5] evtchn: pad struct evtchn to 64 bytes David Vrabel
2015-06-16 9:22 ` Jan Beulich
2015-06-16 11:14 ` Julien Grall
2015-06-16 11:59 ` Jan Beulich
2015-06-16 12:57 ` Julien Grall
2015-06-16 13:13 ` David Vrabel [this message]
2015-06-16 13:27 ` Julien Grall
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