From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
To: Richard Weinberger <richard@nod.at>
Cc: linux-um <linux-um@lists.infradead.org>
Subject: Re: [PATCH] um: allow using glibc string functions instead of generics
Date: Wed, 11 Nov 2020 07:13:45 +0000 [thread overview]
Message-ID: <4b431cfb-8811-371f-9f2a-536861cc2202@cambridgegreys.com> (raw)
In-Reply-To: <1539736322.290788.1605044349917.JavaMail.zimbra@nod.at>
On 10/11/2020 21:39, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
>> Von: "anton ivanov" <anton.ivanov@cambridgegreys.com>
>> An: "richard" <richard@nod.at>
>> CC: "linux-um" <linux-um@lists.infradead.org>
>> Gesendet: Dienstag, 10. November 2020 22:33:48
>> Betreff: Re: [PATCH] um: allow using glibc string functions instead of generics
>
>> On 10/11/2020 21:29, Richard Weinberger wrote:
>>> ----- Ursprüngliche Mail -----
>>>> Von: "anton ivanov" <anton.ivanov@cambridgegreys.com>
>>>>> On what workload did you see such a huge performance improvement?
>>>> File IO ~ 1% or thereabouts, iperf - 2-4%.
>>>>
>>>>> The in-kernel variants of memcpy and such are already well optimized.
>>>> UML has no string.h in asm which means it falls back to
>>>> asm-generic/string.h which in turn pulls in the ones from lib/string.c
>>>>
>>>> These are not optimized.
>>> Hmmm, I think it should use the highly optimized variants from arch/x86.
>>
>> That is the other option - to bring in string32.h and string64.h from x86.
>
> Yes, I thought we do so already. I fear we list this feature after some code
> cleanup a long time ago.
>
> I'm happy with either option.
I will have a look if we lost other optimized code as a result of the
asm cleanup and sort it out in the next version.
The advantage of glibc is that it is guaranteed to chose the correct
flavor for the CPU.
I do not think that this the case for the kernel ones, because they rely
on boottime CPU features detection which does not happen in the case of
UML. So in order to use them properly, we may have to implement that.
Otherwise, the code in the glibc tree and in the kernel is nearly
identical. Just glibc was easier as it did not require figuring out CPU
detection :)
>
> Thanks,
> //richard
>
> _______________________________________________
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> linux-um@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-um
>
--
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/
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next prev parent reply other threads:[~2020-11-11 7:13 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-10 16:30 [PATCH] um: allow using glibc string functions instead of generics anton.ivanov
2020-11-10 16:40 ` Johannes Berg
2020-11-10 16:54 ` Anton Ivanov
2020-11-10 20:13 ` Richard Weinberger
2020-11-10 20:56 ` Anton Ivanov
2020-11-10 21:29 ` Richard Weinberger
2020-11-10 21:33 ` Anton Ivanov
2020-11-10 21:39 ` Richard Weinberger
2020-11-11 7:13 ` Anton Ivanov [this message]
2020-11-11 8:26 ` Anton Ivanov
2020-11-11 15:14 ` Anton Ivanov
2020-11-11 15:59 ` Anton Ivanov
2020-11-11 18:09 ` Anton Ivanov
2020-11-11 9:49 ` Anton Ivanov
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