[Fontconfig] a regression caused by f44bfad235e63bb792c38e16ae1fbd281ec1453b

[Akira TAGOH]

I have no idea to get a better solution for that issue so far.
though it might be gone after ad9f588, we need to test this without it.

On Tue, Jan 5, 2016 at 6:49 PM,  <u-pnrz at aetey.se> wrote:
> Hello,
>
> I have just found out that the commit f44bfad235e63bb792c38e16ae1fbd281ec1453b
> ("Workaround another race condition issue", 2014-06-05)
> leads in certain scenarios to a huge performance regression
> at applications' startup.
>
> The concerned scenario is:
>
>  - static font data
>  - static font configuraton data
>  - pregenerated font caches
>  - font data on a filesystem with an expensive stat()
>    (a network file system with cold metadata cache)
>
> An application using fontconfig with the commit applied seems to issue
> stat() on every font file.
> In a practical test this took about 90 seconds, which is about the
> multiple of the network latency and the number of the available font
> files.
>
> We are using specifically Coda file system, but on networks with
> remarkable latency most remote file systems would behave similarly,
> even if the amount of impact can vary (aggressive prefetching of
> metainformation can mask the issue but is not always good/acceptable).
>
> Note that we try to make as many fonts as possible _available_ at the
> same time and also that most of them are not being _used_ on a single
> given computer, nor have to be pulled into the file system cache over
> the network, not even their stat() information.
>
> We noticed the issue because the GUI login time grew dramatically,
> I could narrow the reason to this commit.
>
> The change was apparently introduced to make fc-cache more
> reliable. Hopefully this can be done differently, without imposing such
> a high cost on the applications startup.
>
> For the moment we have no choice but patch the library, reverting the
> change, to avoid such pathological situations.
>
> It would be very nice to get a better fix upstream.
>
> Thanks,
> Rune
>
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-- 
Akira TAGOH