From: "René Scharfe" <email@example.com> To: "Ævar Arnfjörð Bjarmason" <firstname.lastname@example.org> Cc: Jeff King <email@example.com>, Derrick Stolee <firstname.lastname@example.org>, email@example.com, Yiyuan guo <firstname.lastname@example.org> Subject: Re: [PATCH 3/5] pack-objects: clamp negative window size to 0 Date: Wed, 5 May 2021 18:19:06 +0200 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <firstname.lastname@example.org> Am 05.05.21 um 13:53 schrieb Ævar Arnfjörð Bjarmason: > > On Tue, May 04 2021, René Scharfe wrote: > >> There's another option: Mapping -1 or all negative values to the >> maximum: > That seems sensible to expose, but I think should really be > --window=max, not --window=-1. The latter feels way too much like > assuming that a user might know about C's "set all bits" semantics. Nitpicking: Setting all bits for -1 is done by two's complement, which is just one of the signed number representations supported by C. But yeah: A non-numeric value would probably be better in general. As Peff explained it's not a particularly good idea to specify the maximum values of --depth and --window, though, so no need to make it easier. > The one example of such a variable I could think of is core.abbrev=no, > which could arguably benefit from a core.abbrev=max synonym. core.abbrev=no turns off abbreviation, i.e. you get the full hash size (false and off work as well). Following that logic, core.abbrev=max would ask for a maximum of abbreviation, i.e. for the shortest unambiguous hash. That would have a length of at least 4. This value is stored in a constant called minimum_abbrev -- which seems backwards. The implied negation of abbrev (the more you abbreviate, the shorter the length) is a bit confusing. > Another one is *.threads, e.g. grep.threads, index.threads. We currently > say that "auto" is like "max, but I can see how we'd eventually benefit > from splitting those up. I sometimes run git on machines where that > "auto" is 48 or whatever (I haven't benchmarked, but that's surely > counter-productive). Having max != auto in that case (but still having a > "max") would be nice. Good thinking. What is the maximum number of threads? Certainly higher than the number of CPUs. Would that be useful? Maybe -- on a single-core VM with an SSD queue length of 32 we can probably benefit from running more than one thread. Are our threads CPU-bound or I/O-bound? I guess the answer is "yes". :) How do we even find out the disk queue length in a portable way? And how would we calculate the optimal number of threads? Are these even the right questions to ask? An "auto" option might help with that. I imagine it starting out with some default value and then experimentally decreasing and and increasing the number of threads to find out which one works best. Downside: It would need to have comparable workloads for that. And these benchmarks need an otherwise quiet system. Similar battery level if running on a laptop. Same system temperature. Impractical during normal use. Perhaps a "git benchmark" command that runs some synthetic speed tests to tune grep.threads etc. would be possible? René
next prev parent reply other threads:[~2021-05-05 16:19 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-01 14:02 [PATCH 0/5] pack-objects: better handling of negative options Jeff King 2021-05-01 14:02 ` [PATCH 1/5] t5300: modernize basic tests Jeff King 2021-05-03 5:27 ` Junio C Hamano 2021-05-03 14:53 ` Jeff King 2021-05-01 14:03 ` [PATCH 2/5] t5300: check that we produced expected number of deltas Jeff King 2021-05-01 14:03 ` [PATCH 3/5] pack-objects: clamp negative window size to 0 Jeff King 2021-05-03 12:10 ` Derrick Stolee 2021-05-03 14:55 ` Jeff King 2021-05-04 18:47 ` René Scharfe 2021-05-04 21:38 ` Jeff King 2021-05-05 11:53 ` Ævar Arnfjörð Bjarmason 2021-05-05 16:19 ` René Scharfe [this message] 2021-05-01 14:04 ` [PATCH 4/5] t5316: check behavior of pack-objects --depth=0 Jeff King 2021-05-01 14:04 ` [PATCH 5/5] pack-objects: clamp negative depth to 0 Jeff King 2021-05-03 12:11 ` Derrick Stolee
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