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diff --git a/service_solahart_jakarta_selatan__082122541663/pfinet_timers.mdwn b/service_solahart_jakarta_selatan__082122541663/pfinet_timers.mdwn new file mode 100644 index 00000000..244ca98b --- /dev/null +++ b/service_solahart_jakarta_selatan__082122541663/pfinet_timers.mdwn @@ -0,0 +1,177 @@ +[[!meta copyright="Copyright © 2013, 2014 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!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 :) |