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Date: Tue, 3 Mar 2009 20:25:05 +0100
Message-ID: <761ea48b0903031125n5d97462eu15caa552764789d9@mail.gmail.com>
Subject: Re: [Qemu-devel] sh : performance problem
From: Laurent Desnogues <laurent.desnogues@gmail.com>
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To: qemu-devel@nongnu.org

On Tue, Mar 3, 2009 at 7:57 PM, Lionel Landwerlin
<lionel.landwerlin@openwide.fr> wrote:
> Le mercredi 04 mars 2009 =E0 00:46 +0900, Shin-ichiro KAWASAKI a =E9crit =
:
[...]
>>   sh4 : 5.8 [seconds]     O(n) utlb search.
>>   sh4 : 4.6 [seconds]     O(log2(n)) utlb search.
>>   sh4 : 4.1 [seconds]     O(1) utlb search by Lionel
>>   arm : 0.8 [seconds]     (-M versatilepb + Debian ARM)
>>
>> Your patch has a nice score!
>
> Great :) But we're still far from arm :(

It would be interesting if you could run oprofile of both platforms
(and even better if that was with call-graph output).

>> > +#if !defined(CONFIG_USER_ONLY)
>> > +    /* vpn to utlb entry caches (too much space for user emulation) *=
/
>> > +    uint8_t utlbs_1k[4194304]; /* 222 =3D> 4 Mb */
>> > +    uint8_t utlbs_4k[1048576]; /* 220 =3D> 1 Mb */
>> > +    uint8_t utlbs_64k[65536]; /* 216 =3D> 64 Kb */
>> > +    uint8_t utlbs_1m[4096]; /* 212 =3D> 4 Kb */
>> > +#endif
>> >  } CPUSH4State;
>>
>> Isn't it too gorgeous?
>> How about allocating them on demand?
>> I guess sh-linux uses only utlbs_4k[], in general.
>> If so, 4 Mb utlbs_1k[] is waste.
>>
>
> sh-linux can also use huge pages of 64k and 1M.
>
> I think it is important to keep the emulation as close as possible from
> the real the cpu capabilities.

I think Shin-ichiro was rather pointing a the number of 1k pages,
which are probably not used.  OTOH I agree being close to
CPU capabilities is important.


Laurent