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Re: [PATCH 2/4] S390: Use 64bit instruction to check for copies of > 1MB with mvcle.

From: Stefan Liebler <stli at linux dot vnet dot ibm dot com>
To: libc-alpha at sourceware dot org
Date: Tue, 26 Apr 2016 16:20:31 +0200
Subject: Re: [PATCH 2/4] S390: Use 64bit instruction to check for copies of > 1MB with mvcle.
Authentication-results: sourceware.org; auth=none
References: <1461672469-2107-1-git-send-email-stli at linux dot vnet dot ibm dot com> <1461672469-2107-2-git-send-email-stli at linux dot vnet dot ibm dot com> <571F7826 dot 5050402 at redhat dot com>

On 04/26/2016 04:16 PM, Florian Weimer wrote:

On 04/26/2016 02:07 PM, Stefan Liebler wrote:

The __memcpy_default variant on s390 64bit calculates the number of
256byte blocks in a 64bit register and checks, if they exceed 1MB
to jump to mvcle. Otherwise a mvc-loop is used. The compare-instruction
only checks a 32bit value.
This patch uses a 64bit compare.


This is purely an optimization, right?  Did the previous implementation
still perform a complete copy (although perhaps in a less efficient way)?

Thanks,
Florian

Yes it performs a complete copy with mcv-loop instead of mvcle.

References:
- [PATCH 1/4] S390: Use mvcle for copies > 1MB on 32bit with default memcpy variant.
  - From: Stefan Liebler
- [PATCH 2/4] S390: Use 64bit instruction to check for copies of > 1MB with mvcle.
  - From: Stefan Liebler
- Re: [PATCH 2/4] S390: Use 64bit instruction to check for copies of > 1MB with mvcle.
  - From: Florian Weimer

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