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