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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

  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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