From: Richard Sandiford <richard.sandiford@arm.com>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
Richard Earnshaw <Richard.Earnshaw@arm.com>
Subject: Re: [PATCH][AARCH64] Set jump-align=4 for neoversen1
Date: Mon, 20 Jan 2020 14:33:00 -0000 [thread overview]
Message-ID: <mptd0bew6kn.fsf@arm.com> (raw)
In-Reply-To: <HE1PR0801MB2044729EF78EF2B24B2F8B5B83310@HE1PR0801MB2044.eurprd08.prod.outlook.com> (Wilco Dijkstra's message of "Fri, 17 Jan 2020 16:48:13 +0000")
Wilco Dijkstra <Wilco.Dijkstra@arm.com> writes:
> Hi Kyrill & Richard,
>
>> I was leaving this to others in case it was obvious to them. On the
>> basis that silence suggests it wasn't, :-) could you go into more details?
>> Is it expected on first principles that jump alignment doesn't matter
>> for Neoverse N1, or is this purely based on experimentation? If it's
>
> Jump alignment is set to 4 on almost all cores because higher values have
> a major codesize cost and yet give no performance gains.
>
> I suspect any core that set it higher has done so by accident rather than
> having benchmarked the cost/benefit.
>
>> expected, are we sure that the other "32:16" entries are still worthwhile?
>> When you say it doesn't make a difference in performance, does that mean
>> that no individual test's performance changed significantly, or just that
>> the aggregate score didn't? Did you experiment with anything inbetween
>> the current 32:16 and 4, such as 32:8 or even 32:4?
>
> I mean there is no difference above the noise floor for any test you throw at it.
OK, great. In that case, let's go with the patch as posted.
Thanks,
Richard
> I tried other alignments including 32:16, 32:12, 32:8 but all have a significant
> cost and zero benefit.
>
> Cheers,
> Wilco
prev parent reply other threads:[~2020-01-20 14:23 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-24 16:25 Wilco Dijkstra
2020-01-16 17:53 ` Wilco Dijkstra
2020-01-17 9:25 ` Richard Sandiford
2020-01-17 11:12 ` Kyrill Tkachov
2020-01-17 17:53 ` Wilco Dijkstra
2020-01-20 14:33 ` Richard Sandiford [this message]
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