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From: Eric Sunshine <>
To: Jeff King <>
Cc: Git List <>
Subject: Re: [PATCH 3/3] index-pack: adjust default threading cap
Date: Fri, 21 Aug 2020 14:08:55 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Aug 21, 2020 at 1:58 PM Jeff King <> wrote:
> So what's a good default value? It's clear that the current cap of 3 is
> too low; our default values are 42% and 57% slower than the best times
> on each machine. The results on the 40-core machine imply that 20
> threads is an actual barrier regardless of the number of cores, so we'll
> take that as a maximum. We get the best results on these machines at
> half of the online-cpus value. That's presumably a result of the
> hyperthreading. That's common on multi-core Intel processors, but not
> necessarily elsewhere. But if we take it as an assumption, we can
> perform optimally on hyperthreaded machines and still do much better
> than the status quo on other machines, as long as we never half below
> the current value of 3.

I'm not familiar with the index-pack machinery, so this response may
be silly, but the first question which came to my mind was whether or
not SSD vs. spinning-platter disk impacts these results, and which of
the two you were using for the tests (which I don't think was
mentioned in any of the commit messages). So, basically, I'm wondering
about the implication of this change for those of us still stuck with
old spinning-platter disks.

  reply	other threads:[~2020-08-21 18:09 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-21 17:51 [PATCH 0/3] index-pack threading defaults Jeff King
2020-08-21 17:53 ` [PATCH 1/3] p5302: disable thread-count parameter tests by default Jeff King
2020-08-21 17:54 ` [PATCH 2/3] p5302: count up to online-cpus for thread tests Jeff King
2020-08-21 17:58   ` Jeff King
2020-08-21 17:58 ` [PATCH 3/3] index-pack: adjust default threading cap Jeff King
2020-08-21 18:08   ` Eric Sunshine [this message]
2020-08-21 18:41     ` Jeff King
2020-08-22  1:16   ` brian m. carlson
2020-08-24 17:37     ` Jeff King
2020-08-24 17:55       ` Eric Sunshine
2020-08-21 18:44 ` [PATCH 0/3] index-pack threading defaults Jeff King
2020-08-21 18:59   ` Junio C Hamano
2020-08-21 19:14     ` Jeff King

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