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bug#49107: [PATCH core-updates] gnu: fontconfig: Use (locally) determini
From: |
Ludovic Courtès |
Subject: |
bug#49107: [PATCH core-updates] gnu: fontconfig: Use (locally) deterministic caching |
Date: |
Mon, 12 Jul 2021 10:30:56 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
Hi,
Sarah Morgensen <iskarian@mgsn.dev> skribis:
> Ludovic Courtès <ludo@gnu.org> writes:
[...]
>> Does Fontconfig stats all these files every time an application starts?
>> Did you compare ‘strace -c some app’ with and without this change, to
>> get an idea of what it costs?
>
> I *believe* it does so whenever an application calls FcFontList or such,
> which is usually on startup. I haven't done tracing with an application
> that actually uses FcFontList, but I just now ran a naive test, along
> the lines of:
>
> $ fc-cache -rf
> $ strace -c fc-list
>
> The old fc-list:
>
> % time seconds usecs/call calls errors syscall
> ------ ----------- ----------- --------- --------- ----------------
> 28.50 0.000226 0 228 142 openat
> 22.19 0.000176 1 136 26 access
> 11.10 0.000088 0 133 70 stat
> 5.93 0.000047 0 86 close
> 5.55 0.000044 2 22 fstatfs
> 5.30 0.000042 0 54 37 readlink
> 4.54 0.000036 4 8 munmap
> 3.78 0.000030 0 70 mmap
> 2.65 0.000021 1 20 write
> 2.52 0.000020 0 104 read
> 2.52 0.000020 0 40 fstat
> 1.89 0.000015 1 8 fadvise64
> 1.77 0.000014 1 10 getpid
> 0.88 0.000007 0 10 brk
> 0.63 0.000005 0 35 getrandom
> 0.25 0.000002 2 1 1 ioctl
> 0.00 0.000000 0 15 mprotect
> 0.00 0.000000 0 2 rt_sigaction
> 0.00 0.000000 0 1 rt_sigprocmask
> 0.00 0.000000 0 1 execve
> 0.00 0.000000 0 1 arch_prctl
> 0.00 0.000000 0 1 futex
> 0.00 0.000000 0 4 getdents64
> 0.00 0.000000 0 1 set_tid_address
> 0.00 0.000000 0 1 set_robust_list
> 0.00 0.000000 0 1 prlimit64
> ------ ----------- ----------- --------- --------- ----------------
> 100.00 0.000793 0 993 276 total
>
>
> And the patched fc-list:
>
> % time seconds usecs/call calls errors syscall
> ------ ----------- ----------- --------- --------- ----------------
> 17.19 0.000125 0 126 11 access
> 14.44 0.000105 0 126 52 openat
> 12.24 0.000089 1 55 mmap
> 10.32 0.000075 0 99 read
> 8.67 0.000063 4 15 mprotect
> 8.25 0.000060 0 94 6 newfstatat
> 5.50 0.000040 0 74 close
> 5.23 0.000038 0 58 40 readlink
> 4.68 0.000034 34 1 set_tid_address
> 3.30 0.000024 0 38 getrandom
> 3.16 0.000023 1 13 pread64
> 1.65 0.000012 0 26 getdents64
> 1.51 0.000011 1 9 brk
> 1.10 0.000008 4 2 rt_sigaction
> 0.83 0.000006 0 9 munmap
> 0.55 0.000004 4 1 rt_sigprocmask
> 0.55 0.000004 4 1 prlimit64
> 0.41 0.000003 3 1 arch_prctl
> 0.41 0.000003 3 1 set_robust_list
> 0.00 0.000000 0 20 write
> 0.00 0.000000 0 1 1 ioctl
> 0.00 0.000000 0 1 execve
> 0.00 0.000000 0 1 sysinfo
> 0.00 0.000000 0 11 fstatfs
> 0.00 0.000000 0 8 fadvise64
> ------ ----------- ----------- --------- --------- ----------------
> 100.00 0.000727 0 791 110 total
>
> Now that is unexpected! There are actually less stats and opens. I'm
> stumped! My profile has about 20 font packages (about 450 actual files)
> installed. For reference, for both versions, `fc-cache -rf` yields about
> 3700 stats; and `fc-cache` yeilds about 300...
Well, even better. :-)
I went ahead and applied the patch. ‘fontconfig-minimal’ builds fine;
‘fonconfig’ (with documentation) fails to build its PDF documentation,
but that’s not related to this change.
> I still wish we could address it "properly" by generating a cache at
> profile generation time... but it looks like fontconfig embeds the full
> paths of fonts in the cache (including username, since fonts are under
> ~/.guix-profile), so I doubt such a cache would work. I plan to try it
> eventually anyway (or perhaps someone else will), but in the meantime,
> this looks like the 80% solution.
Yeah. It could be that each font package could contain its own cache,
and the profile hook would just assemble all these caches (provided the
file format makes it possible without too much of a headache).
Thanks!
Ludo’.