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Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself |
Date: |
Sun, 23 May 2010 19:30:39 +0300 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Sun, May 23, 2010 at 07:03:10PM +0300, Avi Kivity wrote:
> On 05/23/2010 06:51 PM, Michael S. Tsirkin wrote:
>>>
>>>> So locked version seems to be faster than unlocked,
>>>> and share/unshare not to matter?
>>>>
>>>>
>>> May be due to the processor using the LOCK operation as a hint to
>>> reserve the cacheline for a bit.
>>>
>> Maybe we should use atomics on index then?
>>
>
> This should only be helpful if you access the cacheline several times in
> a row. That's not the case in virtio (or here).
So why does it help?
> I think the problem is that LOCKSHARE and SHARE are not symmetric, so
> they can't be directly compared.
In what sense are they not symmetric?
>> OK, after adding mb in code patch will be sent separately,
>> the test works for my workstation. locked is still fastest,
>> unshared sometimes shows wins and sometimes loses over shared.
>>
>> address@hidden ~]# ./cachebounce share 0 1
>> CPU 0: share cacheline: 6638521 usec
>> CPU 1: share cacheline: 6638478 usec
>>
>
> 66 ns? nice.
>
>> address@hidden ~]# ./cachebounce share 0 2
>> CPU 0: share cacheline: 14529198 usec
>> CPU 2: share cacheline: 14529156 usec
>>
>
> 140 ns, not too bad. I hope I'm not misinterpreting the results.
>
> --
> error compiling committee.c: too many arguments to function
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, (continued)
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Rusty Russell, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Rusty Russell, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/24
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/24
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/24
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/23
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Rusty Russell, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Avi Kivity, 2010/05/20
- Re: [Qemu-devel] [PATCH RFC] virtio: put last seen used index into ring itself, Michael S. Tsirkin, 2010/05/20
[Qemu-devel] Re: [PATCH RFC] virtio: put last seen used index into ring itself, Ryan Harper, 2010/05/11