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[[!tag open_issue_hurd]]


# IRC, freenode, #hurd, 2013-02-11

    <braunr> now that there is a pthread_hurd_cond_timedwait_np function
      available, we could replace the ulgy timers in pfinet


# IRC, freenode, #hurd, 2013-04-02

    <braunr> youpi: also, i think i know why fakeroot is slow on the hurd
    <braunr> well, pfinet actually
    <youpi> tcp flow control?
    <braunr> i think it's because of our timer resolution
    <youpi> ah
    <braunr> and i think i spotted a small mistake in the timer emulation code
      btw
    <braunr> it's so obvious i even doubt it's actually true :)
    <braunr> see timer_emul.c:timer_function
    <braunr> the code checks for timers->expires < jiffies
    <braunr> shouldn't it be "<="
    <braunr> ?
    <youpi> well it'd be equivalent
    <youpi> if ==, then wait becomes 0 in the else
    <braunr> see the second scheck
    <braunr> the one performed right before running the callback
    <youpi> ah, the while?
    <braunr> yes
    <youpi> I'd say <= could do it yes
    <braunr> ok
    <braunr> i have hurd packages ready to be tested
    <youpi> although I'm unsure it'd make a difference
    <youpi> do you notice some?
    <braunr> just waiting for my current glibc to finish building
    <braunr> and i'll test right after
    <braunr> i think it would actually
    <youpi> in which case?
    <braunr> the timer resolution is 10ms
    <braunr> it's huge
    <braunr> well, i hope it fixes fakeroot slowness :)
    <youpi> so timers below that would trigger immediately?
    <braunr> or equal
    <braunr> taht's the problem
    <braunr> for 10ms, timers that have expired must wait for the next tick to
      fire
    <youpi> I include "equal" in below
    <youpi> actually :)
    <braunr> then yes :)
    <braunr> soryy i never know when equal is implicit
    <youpi> because they boil down to expires = jiffies
    <youpi> in french it's implicit
    <youpi> but anyway here equal is not really important
    <braunr> right
    <braunr> why ?
    <youpi> it's the fact that 1ms would be rounded up to 10ms, not down to 0ms
    <braunr> well, doing that seems reasonable
    <youpi> or rather, rounded down to 0ms, but waited for 10ms because of the
      <
    <braunr> we do want timers not to fire before the time event
    <youpi> I'm however wondering which part of the code would have timer below
      10ms
    <braunr> well, a select with low timeout from a client perhaps ?
    <youpi> but then we have to round up
    <youpi> as you say we don't want to fire before some time
    <braunr> well yes
    <braunr> that's fine
    <youpi> all that being said, linux has been having 10ms clock for a long
      time
    <braunr> but when the timer fires, i.e. when expires == jiffie, we do want
      it to fire
    <youpi> highres timers are only relativeley recent
    <braunr> not at jiffie + 1
    <youpi> braunr: ah, right, so we don't wait for 20ms instead of 10ms
    <braunr> yes
    <youpi> ok, so it's not a miracle fix, but could bring 2times fix
    <braunr> well, pfinet eats 40% of my processor when this problem occurs
    <braunr> which i'm seeing right now
    <youpi> yes, I've seen that too
    <braunr> so it may be a visible win
    <braunr> build finished :) let's see
    <youpi> Mmm, thinking again
    <youpi> indeed
    <youpi> when expires become jiffies
    <youpi> we mach_msg (0)
    <youpi> but don't do anything
    <youpi> and then restart
    <youpi> so just eaten cpu for nothing
    <braunr> is there a small package that builds fast and uses fakeroot a lot
      ?
    <youpi> something like a package which has a lot of data to install at make
      install
    <braunr> or i can rebuild glibc with -nc
    <youpi> ok, I've checked in linux
    <pinotree> libarchive's testsuite used to intermittently failing under
      fakeroot
    <youpi> it's definitely <= which is meant
    <braunr> it looks better
    <braunr> but still not 100% cpu
    <youpi> at any rate, as long as it doesn't seem to break anything, please
      push the fix
    <youpi> it definitely makes sense
    <youpi> (and I don't see why it could break anything)
    <braunr> ok
    <braunr> i'll look into this timer problem a bit more, there may be other
      code involved
    <braunr> yes, schedule_timeout could need a review
    <braunr> actually, fakeroot rm -rf * is a good test
    <braunr> and it's still damn slow


## IRC, freenode, #hurd, 2013-11-04

    <braunr> i think i know why fakeroot is slow no
    <braunr> now
    <braunr> schedule_timeout as implemented in pfinet can only be awaken by a
      timeout
    <braunr> even when the expected even comes in earlier
    <braunr> so yes, the proper solution is to rewrite the timers using
      interruptible_sleep_on_timeout (and in turn
      pthread_hurd_cond_timedwait_np)
    <braunr> hm no, it's still not that straightforward :(


## IRC, freenode, #hurd, 2013-11-05

    <braunr> youpi: i found the bug slowing down fakeroot-tcp
    <braunr> it's actually a bug that slows down anything using the loopback
      device
    <braunr> (although there still is a problem with fakeroot chown)
    <youpi> oh!
    <braunr> basically
    <braunr> the loopback device calls netif_rx from its xmit function
    <braunr> which is perfectly fine
    <braunr> except the glue code makes mark_bh (used to raise bottom halves)
      broadcast a condition
    <braunr> and since netif_rx is called from within xmit, which is called
      from the net_bh worker thread
    <braunr> the thread itself is never waiting for the condition when it is
      broadcast
    <braunr> it's very simple to fix, i'll send a patch later
    <braunr> netcat to netcat now consumes 100% cpu
    <braunr> as does fakeroot ls -Rl
    <braunr> but for some reason fakeroot chown is still extremely slow
    <braunr> and i've seen deadlocks in glibc (e.g. setlocale() getting the
      locale lock, which is locked again in case libfakeroot fails and calls
      strerror)
    <braunr> so still a bit of debugging work needed


## IRC, freenode, #hurd, 2013-11-06

    <braunr> chown being slow with fakeroot-tcp can also be seen on linux

    <teythoon> did your recent patch improve the performance of fakeroot-tcp ?
    <braunr> yes
    <teythoon> very nice :)
    <braunr> but fakeroot chown is still slow
    <braunr> although it's also slow on linux
    <braunr> so i'm not looking into that any more for the time being
    <braunr> as long as it's not used recursively on huge directories, it's
      fine


## IRC, freenode, #hurd, 2013-11-09

    <teythoon> braunr: fakeroot-tcp is indeed much faster now :)