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Date: Wed, 05 Mar 2008 10:47:45 +0100 From: Eric Dumazet <dada1@...mosbay.com> To: David Miller <davem@...emloft.net> Cc: dmantipov@...dex.ru, linux-kernel@...r.kernel.org Subject: Re: Are Linux pipes slower than the FreeBSD ones ? David Miller a écrit : > From: Antipov Dmitry <dmantipov@...dex.ru> > Date: Wed, 05 Mar 2008 10:46:57 +0300 > > >> Despite of this obvious fact, recently I've tried to compare pipe >> performance on Linux and FreeBSD systems. Unfortunately, Linux >> results are poor - ~2x slower than FreeBSD. The detailed description >> of the test case, preparation, environment and results are located >> at http://213.148.29.37/PipeBench, and everyone are pleased to look >> at, reproduce, criticize, etc. >> > > FreeBSD does page flipping into the pipe receiver, so rerun your test > case but have either the sender or the receiver make changes to > their memory buffer in between the read/write calls. > > FreeBSD's scheme is only good for benchmarks, rather then real life. > > > > page flipping might explain differences for big transferts, but note the difference with small buffers (64, 128, 256, 512 bytes) I tried the 'pipe' prog on a fresh linux-2.6.24.2, on a dual Xeon 5120 machine, and we can notice that four cpus are used (but only two threads are running on this benchmark) Cpu0 : 3.7% us, 38.7% sy, 0.0% ni, 57.7% id, 0.0% wa, 0.0% hi, 0.0% si Cpu1 : 4.0% us, 36.5% sy, 0.0% ni, 58.5% id, 1.0% wa, 0.0% hi, 0.0% si Cpu2 : 3.7% us, 25.9% sy, 0.0% ni, 70.4% id, 0.0% wa, 0.0% hi, 0.0% si Cpu3 : 2.0% us, 25.3% sy, 0.0% ni, 72.7% id, 0.0% wa, 0.0% hi, 0.0% si # vmstat 1 10 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 2 0 0 1356432 125788 416796 0 0 3 1 5 2 1 2 97 0 1 0 0 1356432 125788 416796 0 0 0 0 18 336471 5 35 61 0 1 0 0 1356680 125788 416796 0 0 0 0 16 330420 6 34 60 0 1 0 0 1356680 125788 416796 0 0 0 0 16 319826 6 34 61 0 1 0 0 1356680 125788 416796 0 0 0 0 16 311708 5 34 61 0 2 0 0 1356680 125788 416796 0 0 0 0 17 331712 4 35 61 0 1 0 0 1356680 125788 416796 0 0 0 4 17 333001 6 32 62 0 1 0 0 1356680 125788 416796 0 0 0 0 15 336755 7 31 62 0 2 0 0 1356680 125788 416796 0 0 0 0 16 323086 5 34 61 0 1 0 0 1356680 125788 416796 0 0 0 0 12 373822 4 33 63 0 # opreport -l /boot/vmlinux-2.6.24.2 |head -n 30 CPU: Core 2, speed 1866.8 MHz (estimated) Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000 samples % symbol name 52137 9.3521 kunmap_atomic 50983 9.1451 mwait_idle_with_hints 50448 9.0492 system_call 49727 8.9198 task_rq_lock 24531 4.4003 pipe_read 19820 3.5552 pipe_write 16176 2.9016 dnotify_parent 15455 2.7723 file_update_time 15216 2.7294 find_busiest_group 12449 2.2331 __copy_from_user_ll_nozero 12291 2.2047 set_next_entity 12023 2.1566 resched_task 11728 2.1037 __switch_to 11294 2.0259 update_curr 10749 1.9281 touch_atime 9334 1.6743 kmap_atomic_prot 9084 1.6295 __wake_up_sync 8321 1.4926 try_to_wake_up 7522 1.3493 pick_next_entity 7216 1.2944 cpu_idle 6780 1.2162 vfs_read 6727 1.2067 vfs_write 6570 1.1785 __copy_to_user_ll 6407 1.1493 syscall_exit 6283 1.1270 restore_nocheck 6064 1.0877 weighted_cpuload 6045 1.0843 rw_verify_area This benchmarek mostly stress scheduler AFAIK, not really pipe() code... Lot of context switches... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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