Re: [Qemu-devel] sh : performance problem

[Shin-ichiro KAWASAKI <kawasaki@juno.dti.ne.jp>]

Lionel Landwerlin wrote:
> Le mardi 03 mars 2009 à 20:25 +0100, Laurent Desnogues a écrit :
>> On Tue, Mar 3, 2009 at 7:57 PM, Lionel Landwerlin
>> <lionel.landwerlin@openwide.fr> wrote:
>>> Le mercredi 04 mars 2009 à 00:46 +0900, Shin-ichiro KAWASAKI a écrit :
>> [...]
>>>>   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 => 4 Mb */
>>>>> +    uint8_t utlbs_4k[1048576]; /* 220 => 1 Mb */
>>>>> +    uint8_t utlbs_64k[65536]; /* 216 => 64 Kb */
>>>>> +    uint8_t utlbs_1m[4096]; /* 212 => 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.
> 
> The problem is, when a virtual address space must be resolved, the cpu
> emulator is not able to know what page size has been (or not) used to
> map the address. Thus we must handle the worst case...
> 
> And after all, 5Mb isn't so much, considering the fact that the physical
> guest memory, in system emulation, can be mapped anywhere in the host
> virtual address space, contrary to the user emulation that have harder
> contraints...

IMO, it will be another patch which introduces lines like this.

  if (!env->utlbs_1k)
       env->utlbs_1k = qemu_mallocz(4194304);

But footprint tuning can be left as future task.
Sorry for being too critical.

Regards,
Shin-ichiro KAWASAKI