Package: emacs;
Reported by: Ihor Radchenko <yantar92 <at> posteo.net>
Date: Thu, 24 Aug 2023 10:00:02 UTC
Severity: wishlist
Tags: patch
Message #8 received at 65491 <at> debbugs.gnu.org (full text, mbox):
From: Eli Zaretskii <eliz <at> gnu.org> To: Ihor Radchenko <yantar92 <at> posteo.net>, Stefan Monnier <monnier <at> iro.umontreal.ca> Cc: 65491 <at> debbugs.gnu.org Subject: Re: bug#65491: [PATCH] Improve performance allocating vectors Date: Sat, 26 Aug 2023 10:14:28 +0300
> From: Ihor Radchenko <yantar92 <at> posteo.net> > Date: Thu, 24 Aug 2023 09:59:33 +0000 > > Following up the bignum performance discussion in > https://yhetil.org/emacs-devel/87bkfdsmde.fsf <at> localhost > > This patch adds a heuristic that reduces the time spent searching > `vector_free_lists' when trying to allocate a new vector. > > `vector_free_lists' is a rather long array with few hundreds of > elements. And it does not make sense to check the whole array in > `allocate_vector_from_block' if we can get information about free vector > that was recently made available of if we know for sure that no free > vectors are available (after GC). > > In the patch, we start searching `vector_free_lists' no earlier than the > last known index of the available free vector, or skip the search > entirely when there is known index (after sweep). > > The described approach may sometimes miss free vectors in > `vector_free_lists', especially if the allocation happens from larger > vector to smaller. The cost will be slightly higher memory consumption - > no larger than VECTOR_MAX_FREE_LIST_INDEX extra free vectors. > > With the patch, CPU time spent allocating new vectors in the fib.eln > test from https://yhetil.org/emacs-devel/87bkfdsmde.fsf <at> localhost drops 10x. > > Also, the patch gives a noticeable improvement when running > elisp-benchmarks (ELPA package). The overall speedup is around 10% > (including unaffected tests). > > No single test gets worse within error margins and the following tests > get a significant speedup: > > - eieio 1.32±0.04 -> 1.04±0.03 > - pack-unpack 0.40±0.00 -> 0.35±0.01 > - pidigits 6.00±0.06 -> 4.08±0.12 > > pidigits is no surprise as it likely uses bignums. > > * Results without the patch > > | test | non-gc avg (s) | gc avg (s) | gcs avg | tot avg (s) | tot avg err (s) | > |--------------------+----------------+------------+---------+-------------+-----------------| > | bubble | 0.68 | 0.06 | 1 | 0.73 | 0.05 | > | bubble-no-cons | 1.17 | 0.00 | 0 | 1.17 | 0.07 | > | bytecomp | 1.64 | 0.32 | 13 | 1.95 | 0.03 | > | dhrystone | 2.13 | 0.00 | 0 | 2.13 | 0.02 | > | eieio | 1.19 | 0.13 | 7 | 1.32 | 0.04 | > | fibn | 0.00 | 0.00 | 0 | 0.00 | 0.00 | > | fibn-named-let | 1.47 | 0.00 | 0 | 1.47 | 0.04 | > | fibn-rec | 0.00 | 0.00 | 0 | 0.00 | 0.00 | > | fibn-tc | 0.00 | 0.00 | 0 | 0.00 | 0.00 | > | flet | 1.41 | 0.00 | 0 | 1.41 | 0.03 | > | inclist | 0.84 | 0.00 | 0 | 0.84 | 0.03 | > | inclist-type-hints | 0.76 | 0.00 | 0 | 0.76 | 0.00 | > | listlen-tc | 0.12 | 0.00 | 0 | 0.12 | 0.01 | > | map-closure | 5.25 | 0.00 | 0 | 5.25 | 0.02 | > | nbody | 1.47 | 0.15 | 1 | 1.62 | 0.07 | > | pack-unpack | 0.38 | 0.02 | 1 | 0.40 | 0.00 | > | pack-unpack-old | 1.13 | 0.05 | 3 | 1.19 | 0.03 | > | pcase | 1.77 | 0.00 | 0 | 1.77 | 0.01 | > | pidigits | 5.04 | 0.97 | 17 | 6.00 | 0.06 | > | scroll | 0.58 | 0.00 | 0 | 0.58 | 0.02 | > | smie | 1.47 | 0.05 | 2 | 1.52 | 0.02 | > |--------------------+----------------+------------+---------+-------------+-----------------| > | total | 28.49 | 1.74 | 45 | 30.23 | 0.16 | > > * Results with the patch > > | test | non-gc avg (s) | gc avg (s) | gcs avg | tot avg (s) | tot avg err (s) | > |--------------------+----------------+------------+---------+-------------+-----------------| > | bubble | 0.69 | 0.05 | 1 | 0.74 | 0.07 | > | bubble-no-cons | 1.03 | 0.00 | 0 | 1.03 | 0.02 | > | bytecomp | 1.45 | 0.25 | 13 | 1.70 | 0.10 | > | dhrystone | 1.98 | 0.00 | 0 | 1.98 | 0.05 | > | eieio | 0.92 | 0.12 | 7 | 1.04 | 0.03 | > | fibn | 0.00 | 0.00 | 0 | 0.00 | 0.00 | > | fibn-named-let | 1.45 | 0.00 | 0 | 1.45 | 0.12 | > | fibn-rec | 0.00 | 0.00 | 0 | 0.00 | 0.00 | > | fibn-tc | 0.00 | 0.00 | 0 | 0.00 | 0.00 | > | flet | 1.39 | 0.00 | 0 | 1.39 | 0.07 | > | inclist | 0.83 | 0.00 | 0 | 0.83 | 0.03 | > | inclist-type-hints | 0.77 | 0.00 | 0 | 0.77 | 0.03 | > | listlen-tc | 0.10 | 0.00 | 0 | 0.10 | 0.00 | > | map-closure | 5.25 | 0.00 | 0 | 5.25 | 0.37 | > | nbody | 1.45 | 0.16 | 1 | 1.60 | 0.05 | > | pack-unpack | 0.33 | 0.02 | 1 | 0.35 | 0.01 | > | pack-unpack-old | 1.07 | 0.06 | 3 | 1.13 | 0.08 | > | pcase | 1.78 | 0.00 | 0 | 1.78 | 0.05 | > | pidigits | 3.15 | 0.92 | 17 | 4.08 | 0.12 | > | scroll | 0.55 | 0.00 | 0 | 0.55 | 0.01 | > | smie | 1.45 | 0.04 | 2 | 1.49 | 0.06 | > |--------------------+----------------+------------+---------+-------------+-----------------| > | total | 25.63 | 1.62 | 45 | 27.25 | 0.45 | > Stefan, any comments? my comment is that the savings are quite small, so it seems, so I'm not sure we should install this.
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