From: Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
To: Ihor Radchenko <yantar92@posteo.net>
Cc: 65491@debbugs.gnu.org
Subject: bug#65491: [PATCH] Improve performance allocating vectors
Date: Sun, 27 Aug 2023 12:21:30 -0400 [thread overview]
Message-ID: <jwvsf8479sv.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <87y1i0iwvu.fsf@localhost> (Ihor Radchenko's message of "Thu, 24 Aug 2023 09:59:33 +0000")
> This patch adds a heuristic that reduces the time spent searching
> `vector_free_lists' when trying to allocate a new vector.
The microbenchmarks give surprisingly good performance improvements.
> `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).
Hmm... after GC we should usually have a non-zero number of free vectors
available (the unused parts of vector blocks which could not be `free`d
because they still contain a live vector), no?
[ See comment below. ]
> The described approach may sometimes miss free vectors in
> `vector_free_lists', especially if the allocation happens from larger
> vector to smaller.
Right, it could lead to an increase in fragmentation, tho it might tend
to allocate temporally related objects together, which might be beneficial.
> - pack-unpack 0.40±0.00 -> 0.35±0.01
Interesting. I didn't expect such a large effect there.
> @@ -3145,6 +3145,7 @@ large_vector_vec (struct large_vector *p)
>
> static struct Lisp_Vector *vector_free_lists[VECTOR_MAX_FREE_LIST_INDEX];
>
> +static ptrdiff_t last_known_vector_free_idx = VECTOR_MAX_FREE_LIST_INDEX;
> /* Singly-linked list of large vectors. */
>
> static struct large_vector *large_vectors;
There's clearly some spacing issue with the following comment but more
importantly the new var would need a good comment explaining what the
variable should hold and why it's useful, so we know when it's safe and
desirable to set or use the var.
> @@ -3180,6 +3181,7 @@ setup_on_free_list (struct Lisp_Vector *v, ptrdiff_t nbytes)
> set_next_vector (v, vector_free_lists[vindex]);
> ASAN_POISON_VECTOR_CONTENTS (v, nbytes - header_size);
> vector_free_lists[vindex] = v;
> + last_known_vector_free_idx = vindex;
> }
>
> /* Get a new vector block. */
> @@ -3234,7 +3236,7 @@ allocate_vector_from_block (ptrdiff_t nbytes)
> /* Next, check free lists containing larger vectors. Since
> we will split the result, we should have remaining space
> large enough to use for one-slot vector at least. */
> - for (index = VINDEX (nbytes + VBLOCK_BYTES_MIN);
> + for (index = max (VINDEX (nbytes + VBLOCK_BYTES_MIN), last_known_vector_free_idx);
> index < VECTOR_MAX_FREE_LIST_INDEX; index++)
> if (vector_free_lists[index])
> {
IIUC that's the core of your patch. Nice.
> @@ -3426,6 +3428,7 @@ sweep_vectors (void)
> gcstat.total_vectors = 0;
> gcstat.total_vector_slots = gcstat.total_free_vector_slots = 0;
> memset (vector_free_lists, 0, sizeof (vector_free_lists));
> + last_known_vector_free_idx = VECTOR_MAX_FREE_LIST_INDEX;
>
> /* Looking through vector blocks. */
Hmm... so I was wrong and after GC there are aren't any free vectors?
I need to go re-read that code, then, because it doesn't match my mental
model of how it work(s|ed).
Stefan
next prev parent reply other threads:[~2023-08-27 16:21 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-24 9:59 bug#65491: [PATCH] Improve performance allocating vectors Ihor Radchenko
2023-08-26 7:14 ` Eli Zaretskii
2023-08-26 7:27 ` Ihor Radchenko
2023-08-26 7:31 ` Eli Zaretskii
2023-08-26 7:51 ` Ihor Radchenko
2023-08-26 8:07 ` Ihor Radchenko
2023-08-26 9:01 ` Eli Zaretskii
2023-08-26 7:47 ` Ihor Radchenko
2023-08-26 12:01 ` Mattias Engdegård
2023-08-26 14:54 ` Ihor Radchenko
2023-08-26 14:55 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-27 9:54 ` Mattias Engdegård
2023-09-16 14:58 ` Mattias Engdegård
2023-09-16 16:12 ` Eli Zaretskii
2023-09-16 16:17 ` Eli Zaretskii
2023-09-16 16:32 ` Mattias Engdegård
2023-09-16 16:54 ` Eli Zaretskii
2023-09-16 17:03 ` Mattias Engdegård
2023-09-16 17:11 ` Eli Zaretskii
2023-09-17 3:02 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-17 17:02 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-18 2:19 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-18 2:27 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-18 3:08 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-18 4:10 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-09-16 16:54 ` Mattias Engdegård
2023-09-16 17:09 ` Eli Zaretskii
2023-09-16 17:22 ` Mattias Engdegård
2023-09-16 18:19 ` Eli Zaretskii
2023-09-16 19:04 ` Mattias Engdegård
2023-09-16 19:46 ` Paul Eggert
2023-09-17 5:18 ` Eli Zaretskii
2023-09-17 15:22 ` Paul Eggert
2023-09-17 16:15 ` Eli Zaretskii
2023-09-17 16:37 ` Paul Eggert
2023-09-17 16:44 ` Eli Zaretskii
2023-09-18 16:10 ` Mattias Engdegård
2023-09-18 17:13 ` Eli Zaretskii
2023-09-19 13:28 ` Mattias Engdegård
2023-09-19 14:04 ` Eli Zaretskii
2023-09-19 14:05 ` Mattias Engdegård
2023-09-25 16:06 ` Mattias Engdegård
2023-08-27 16:21 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors [this message]
2023-08-28 10:14 ` Ihor Radchenko
2023-08-28 16:32 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-08-28 12:47 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
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