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SubjectRe: Are Linux pipes slower than the FreeBSD ones ?
David Miller a écrit :
> From: Antipov Dmitry <dmantipov@yandex.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...







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