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Re: [PATCH 4/6] Add new log2 implementation
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Szabolcs Nagy <szabolcs dot nagy at arm dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>, <nd at arm dot com>
- Date: Wed, 27 Jun 2018 15:47:23 +0000
- Subject: Re: [PATCH 4/6] Add new log2 implementation
- References: <77536c53-496b-9b8b-88fd-f7bf4312c1c2@arm.com>
On Wed, 27 Jun 2018, Szabolcs Nagy wrote:
> Improvements on Cortex-A72 compared to current glibc master:
> latency: 2.0x
> thruput: 1.9x
Could you clarify this testing more? If you were testing on AArch64, this
patch should have resulted in no changes at all to performance, because
AArch64 uses sysdeps/ieee754/dbl-64/wordsize-64/e_log2.c and you're not
changing or removing the wordsize-64 version in this patch.
(I expect it would make sense for this patch to remove the wordsize-64
version. Generically, it might make sense to see if the dbl-64 functions
are actually any better for 32-bit systems than the dbl-64/wordsize-64
versions - if GCC is good enough at generating code for the wordsize-64
versions on 32-bit systems, reducing the number of variants by using some
or all of the wordsize-64 versions also on 32-bit systems might make
sense.)
--
Joseph S. Myers
joseph@codesourcery.com