From: Florian Weimer <fweimer@redhat.com>
To: munroesj@linux.vnet.ibm.com
Cc: Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>,
libc-alpha@sourceware.org
Subject: Re: [PATCH] powerpc: Use aligned stores in memset
Date: Tue, 12 Sep 2017 17:04:00 -0000 [thread overview]
Message-ID: <fcf15935-1cbe-7e2b-5364-366b0c52e3f6@redhat.com> (raw)
In-Reply-To: <1505225800.12360.28.camel@oc7878010663>
On 09/12/2017 04:16 PM, Steven Munroe wrote:
> On Tue, 2017-09-12 at 16:08 +0200, Florian Weimer wrote:
>> * Steven Munroe:
>>
>>>> This means that GCC introduced an unaligned store, no matter how memset
>>>> was implemented.
>>>>
>>> C will do what ever the programmer wants. We can not stop that.
>>
>> That's not true. If some specification says that for POWER, mem* must
>> behave in a certain way, and the GCC/glibc combiniation does not do
>> that, that's a bug on POWER.
>>
> What is the bug that you think we are not fixing?
memset, as called by the C programmer, still uses unaligned stores.
>> The programmer only sees the entire toolchain, and it is our job to
>> make the whole thing compliant with applicable specifications, even if
>> this means coordinating among different projects.
>>
>>> And in user mode and cache coherent memory this is not a problem as
>>> Adhemerval explained.
>>
>> Obviously not, otherwise we wouldn't be changing glibc.
>>
> I was arguing against forcing GCC and compilers in general being forced
> to be aware of Cache Inhibited memory. Programmers do.
Exactly. In order to give programmers this choice, you need functions
like device_memset, which are not subject to compiler or library
optimizations which are not valid for device memory.
> What are you arguing?
If you want a memset which is compatible with device memory, you need to
fix GCC *and* glibc. Just patching glibc is not enough because GCC
optimizes memset in ways that are incompatible with your apparent goal..
Thanks,
Florian
next prev parent reply other threads:[~2017-09-12 17:04 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-18 5:13 Rajalakshmi Srinivasaraghavan
2017-08-18 6:21 ` Florian Weimer
2017-08-18 6:51 ` Rajalakshmi Srinivasaraghavan
2017-08-18 9:10 ` Florian Weimer
2017-08-18 12:13 ` Adhemerval Zanella
2017-09-12 10:30 ` Florian Weimer
2017-09-12 12:18 ` Zack Weinberg
2017-09-12 13:57 ` Steven Munroe
2017-09-12 14:37 ` Joseph Myers
2017-09-12 15:06 ` Zack Weinberg
2017-09-12 17:09 ` Florian Weimer
2017-09-12 13:38 ` Steven Munroe
2017-09-12 14:08 ` Florian Weimer
2017-09-12 14:16 ` Steven Munroe
2017-09-12 17:04 ` Florian Weimer [this message]
2017-09-12 19:21 ` Steven Munroe
2017-09-12 19:45 ` Florian Weimer
2017-09-12 20:25 ` Steven Munroe
2017-09-13 13:12 ` Tulio Magno Quites Machado Filho
2017-09-18 13:54 ` Florian Weimer
2017-10-03 18:29 ` Adhemerval Zanella
2017-10-05 12:13 ` Rajalakshmi Srinivasaraghavan
2017-11-08 18:52 ` Tulio Magno Quites Machado Filho
2017-12-08 19:52 ` [PATCHv2] powerpc: POWER8 memcpy optimization for cached memory Tulio Magno Quites Machado Filho
2017-12-08 20:06 ` Florian Weimer
2017-12-11 12:44 ` Tulio Magno Quites Machado Filho
2017-12-11 20:09 ` Adhemerval Zanella
2017-12-10 7:11 ` Rajalakshmi Srinivasaraghavan
2017-12-11 19:48 ` Tulio Magno Quites Machado Filho
2017-08-18 6:25 ` [PATCH] powerpc: Use aligned stores in memset Andrew Pinski
2017-08-21 2:20 ` Tulio Magno Quites Machado Filho
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