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Re: [Qemu-devel] [PATCH v2 05/10] target-arm: optimize arm load/store mu
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH v2 05/10] target-arm: optimize arm load/store multiple ops |
Date: |
Tue, 27 Oct 2009 10:00:01 +0100 |
User-agent: |
Mozilla-Thunderbird 2.0.0.22 (X11/20090707) |
address@hidden a écrit :
> On Oct 27, 2009, at 10:39, ext Aurelien Jarno wrote:
>
>> On Sat, Oct 24, 2009 at 03:19:04PM +0300, address@hidden
>> wrote:
>>> From: Juha Riihimäki <address@hidden>
>>>
>>> RM load/store multiple instructions can be slightly optimized by
>>> loading the register offset constant into a variable outside the
>>> register loop and using the preloaded variable inside the loop
>>> instead
>>> of reloading the offset value to a temporary variable on each loop
>>> iteration. This causes less TCG ops to be generated for a ARM load/
>>> store multiple instruction if there are more than one register
>>> accessed, otherwise the number of generated TCG ops is the same.
>>>
>>> Signed-off-by: Juha Riihimäki <address@hidden>
>>> Acked-by: Laurent Desnogues <address@hidden>
>> This patch breaks, the boot of an arm kernel, as tmp2 is used
>> elsewhere
>> within this code path.
>
> True, I just noticed that as well. This is because the resource leak
> patch
> was refactored to utilize tmp2 inside the loop as well. I just sent a
> new
> revision of this patch that uses tmp3 for th constant value.
>
>> OTOH, while it reduce the number of TCG ops, that should not impact
>> the
>> generated host asm code, as most (all ?) targets are able to add a
>> small constant value to a register in one instruction.
>
> This is true, but I still think it provides a small speed gain as
> there are
> less TCG ops to be processed when generating host code...?
It means less TCG ops, but one more temp variable, therefore if there is
a gain, I don't think it is something even measurable.
OTOH it makes the code a bit more complex to read. I am not really
opposed to this patch (and the other patches of the same kind), but I
will need some more arguments to convince me.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net
[Qemu-devel] [PATCH v2 07/10] target-arm: optimize thumb2 load/store multiple ops, juha . riihimaki, 2009/10/24
[Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, juha . riihimaki, 2009/10/24
- Re: [Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, Laurent Desnogues, 2009/10/25
- Re: [Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, Juha.Riihimaki, 2009/10/26
- Re: [Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, Laurent Desnogues, 2009/10/26
- Re: [Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, Aurelien Jarno, 2009/10/26
- Re: [Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, Juha.Riihimaki, 2009/10/29
- Re: [Qemu-devel] [PATCH v2 09/10] target-arm: optimize neon vld/vst ops, Laurent Desnogues, 2009/10/29