* [PATCH] Fix a hash lookup problem in xfaces.c
@ 2022-01-01 9:24 Zhehao Lin
2022-01-01 9:59 ` Eli Zaretskii
0 siblings, 1 reply; 3+ messages in thread
From: Zhehao Lin @ 2022-01-01 9:24 UTC (permalink / raw)
To: emacs-devel
Hello, this patch fixes a problem in the `face_for_font` function in `src/
xfaces.c` where an `unsigned` instead of an `uintptr_t` was used to
store the
computed hash value of the face. If the hash value was too large (>UINT_MAX)
and truncated, the lookup and storing (the latter uses `uintptr_t` as
the rest
of the program does) would happen in different buckets, resulting in
constant
cache misses.
This can cause huge performance impact when `face_for_font' is called really
frequently (for example with ligatures enabled), but for brevity please
allow
me to omit the details here.
Zhehao Lin
From 06caba2dc34d8ffddd9917f0621d31317e899e90 Mon Sep 17 00:00:00 2001
From: Zhehao Lin <zh_lin1@outlook.com>
Date: Sat, 1 Jan 2022 16:19:49 +0800
Subject: [PATCH] * src/xfaces.c: Use uintptr_t instead of unsigned to store
hash value
---
src/xfaces.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/xfaces.c b/src/xfaces.c
index 6f52637e91..ae6143b330 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -4806,7 +4806,7 @@ face_for_font (struct frame *f, Lisp_Object
font_object,
struct face *base_face)
{
struct face_cache *cache = FRAME_FACE_CACHE (f);
- unsigned hash;
+ uintptr_t hash;
int i;
struct face *face;
--
2.34.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH] Fix a hash lookup problem in xfaces.c
@ 2022-01-01 9:52 Zhehao Lin
0 siblings, 0 replies; 3+ messages in thread
From: Zhehao Lin @ 2022-01-01 9:52 UTC (permalink / raw)
To: emacs-devel
[-- Attachment #1: Type: text/plain, Size: 602 bytes --]
Hello, this patch fixes a problem in the `face_for_font` function in `src/
xfaces.c` where an `unsigned` instead of an `uintptr_t` was used to
store the
computed hash value of the face. If the hash value was too large (>UINT_MAX)
and truncated, the lookup and storing (the latter uses `uintptr_t` as
the rest
of the program does) would happen in different buckets, resulting in
constant
cache misses.
This can cause huge performance impact when `face_for_font' is called really
frequently (for example with ligatures enabled), but for brevity please
allow
me to omit the details here.
Zhehao Lin
[-- Attachment #2: 0001-src-xfaces.c-Use-uintptr_t-instead-of-unsigned-to-st.patch --]
[-- Type: text/x-patch, Size: 681 bytes --]
From 06caba2dc34d8ffddd9917f0621d31317e899e90 Mon Sep 17 00:00:00 2001
From: Zhehao Lin <zh_lin1@outlook.com>
Date: Sat, 1 Jan 2022 16:19:49 +0800
Subject: [PATCH] * src/xfaces.c: Use uintptr_t instead of unsigned to store
hash value
---
src/xfaces.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/xfaces.c b/src/xfaces.c
index 6f52637e91..ae6143b330 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -4806,7 +4806,7 @@ face_for_font (struct frame *f, Lisp_Object font_object,
struct face *base_face)
{
struct face_cache *cache = FRAME_FACE_CACHE (f);
- unsigned hash;
+ uintptr_t hash;
int i;
struct face *face;
--
2.34.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] Fix a hash lookup problem in xfaces.c
2022-01-01 9:24 [PATCH] Fix a hash lookup problem in xfaces.c Zhehao Lin
@ 2022-01-01 9:59 ` Eli Zaretskii
0 siblings, 0 replies; 3+ messages in thread
From: Eli Zaretskii @ 2022-01-01 9:59 UTC (permalink / raw)
To: Zhehao Lin; +Cc: emacs-devel
> Date: Sat, 1 Jan 2022 17:24:27 +0800
> From: Zhehao Lin <zh_lin1@outlook.com>
>
> Hello, this patch fixes a problem in the `face_for_font` function in `src/
> xfaces.c` where an `unsigned` instead of an `uintptr_t` was used to
> store the
> computed hash value of the face. If the hash value was too large (>UINT_MAX)
> and truncated, the lookup and storing (the latter uses `uintptr_t` as
> the rest
> of the program does) would happen in different buckets, resulting in
> constant
> cache misses.
Thanks, installed on the emacs-28 branch.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-01-01 9:59 ` Eli Zaretskii
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