Hi, On Feb 1, 2011, at 1:37 PM, Slawa Olhovchenkov wrote:
> On Sat, Jan 29, 2011 at 07:52:11AM +1100, Bruce Evans wrote: > >>>> there are profiling tools that you may decide to run. >>> >>> What tools I can use on amd64? >>> >>> I boot kernel configured with 'config -p'. >>> Most time in spinlock_exit and acpi_cpu_c1. >> >> Normal profiling works poorly (I see you found my old mail about high >> resolution profiling). Linux might be misreporting the overhead for >> exactly the same reasons that normal profiling works poorly: >> - the profiling clock frequency of ~1 KHz was adequate for 5 MHz machines >> in 1998, but is now too slow. Statistics clocks are even slower (128 >> Hz in FreeBSD, and possibly 100 Hz (?) jiffies in Linux). >> - the statistics clock might be too synchronized with other interrupts. >> The above spinlock_exit and acpi_cpu_c1 times indicate that the >> statistics clock almost always fires on exit from another spinlock >> and/or inside ACPI, for waking up from idle for the latter. Seeing >> lots of exits from spinlocks may indicated that spinlocks are being >> used too much. >> But FreeBSD will report interrupt times and system for non-fast-interrupts >> to an accuracy of about 1 microsecond, since it doesn't use the >> statistics clock much for this. OTOH, for fast interrupts it is typical >> behaviour in FreeBSD and Linux to not see them at all from the statistics >> clock interrupt, since they mask all interrupts so they mask the >> statistics clock interrupt in particular. In FreeBSD, lots of time >> apparently spent in spinlock_exit is a typical result of this, or at >> least similar things, since spinlock_enter masks all interrupts (except >> in my version of course). Linux doesn't have fast interrupts in the >> same way that FreeBSD does, but at least in old versions almost all of >> its interrupts masked other interrupts a lot. > > I do some more test and build kernel with KTR. > Now I don't think that inetrrupt overhead on FreeBSD weight: I try > polling and don't see any difference. > > I see many reported by netperf send errors. I found this > http://docs.freebsd.org/cgi/mid.cgi?E1Aice9-0002by-00. > > After insert into src/nettest_bsd.c usleep(1000) if ENOBUF I see 53% > idle and ./loop 2000000000 "Elapsed 15188006 us" -- this near to linux > (Elapsed 14107670 us). > > 10% of difference may be by more weight network stack (only 32104 > ticks from 126136 in interrupt handler and task switching, and 94032 > -- UDP processing in network stack and passing datagram to driver). > May be weight SOCKBUF_LOCK/SOCKBUF_UNLOCK and/or > INP_INFO_RUNLOCK/INP_RUNLOCK. Try to run with the same network buffers on FreeBSD and Linux. I think, the default values in freebsd are much, much lower. Also in the past ENOBUF was not handled properly in linux. http://wiki.freebsd.org/AvoidingLinuxisms - Do not rely on Linux-specific socket behaviour. In particular, default socket buffer sizes are different (call setsockopt() with SO_SNDBUF and SO_RCVBUF), and while Linux's send() blocks when the socket buffer is full, FreeBSD's will fail and set ENOBUFS in errno. -- Best Wishes, Stefan Lambrev ICQ# 24134177 _______________________________________________ freebsd-performance@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-performance To unsubscribe, send any mail to "freebsd-performance-unsubscr...@freebsd.org"
