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Date: Tue, 25 Sep 2018 16:32:39 -0700
From: subhra mazumdar <subhra.mazumdar@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, tglx@...utronix.de, dhaval.giani@...cle.com,
steven.sistare@...cle.com
Subject: [RFC PATCH v2 0/1] Pipe busy wait
This patch introduces busy waiting for pipes similar to network sockets.
When pipe is full or empty a thread busy waits for some microseconds before
sleeping. This avoids the sleep and wakeup overhead and improves
performance in case wakeup happens very fast. It uses a new field in
pipe_inode_info to decide how much to spin. As different workloads on
different systems can have different optimum spin time, it is configurable
via a tunable that can be set via /proc. The default value is 0 which
indicates no spin.
Following are the hackbench process using pipe and Unixbench performance
numbers with baseline and suitable spin time.
Hackbench on 2 socket, 36 core and 72 threads Intel x86 machine
(lower is better). It also shows the usr+sys time as shown by time:
groups baseline usr+sys patch(spin=10us) usr+sys
1 0.6742 17.0212 0.6842 (-1.48%) 20.2765
2 0.7794 35.1954 0.7116 (8.7%) 38.1318
4 0.9744 55.6513 0.8247 (15.36%) 50.301
8 2.0382 129.519 1.572 (22.87%) 103.722
16 5.5712 427.096 2.7989 (49.76%) 194.162
24 7.9314 566.327 3.962 (50.05%) 278.368
Unixbench on 2 socket, 36 core and 72 threads Intel x86 machine (higher is
better). It shows pipe-based context switching test improving by 107.7% for
1 copy and by 51.3% for 72 parallel copies. This is expected as context
switch overhead is avoided altogether by busy wait.
72 CPUs in system; running 1 parallel copy of tests
System Benchmarks Index Values baseline patch(spin=10us)
Dhrystone 2 using register variables 2837.5 2842.0
Double-Precision Whetstone 753.3 753.5
Execl Throughput 1056.8 1079.2
File Copy 1024 bufsize 2000 maxblocks 1794.0 1805.4
File Copy 256 bufsize 500 maxblocks 1111.4 1117.6
File Copy 4096 bufsize 8000 maxblocks 4136.7 4091.7
Pipe Throughput 752.9 753.3
Pipe-based Context Switching 372.2 772.9
Process Creation 840.1 847.6
Shell Scripts (1 concurrent) 1771.0 1747.5
Shell Scripts (8 concurrent) 7316.6 7308.3
System Call Overhead 578.0 578.0
======== ========
System Benchmarks Index Score 1337.8 1424.0
72 CPUs in system; running 72 parallel copies of tests
System Benchmarks Index Values baseline patch(spin=10us)
Dhrystone 2 using register variables 112849.7 112429.8
Double-Precision Whetstone 44971.1 44929.7
Execl Throughput 11257.6 11258.7
File Copy 1024 bufsize 2000 maxblocks 1514.6 1471.3
File Copy 256 bufsize 500 maxblocks 919.8 917.4
File Copy 4096 bufsize 8000 maxblocks 3543.8 3355.5
Pipe Throughput 34530.6 34492.9
Pipe-based Context Switching 11298.2 17089.9
Process Creation 9422.5 9408.1
Shell Scripts (1 concurrent) 38764.9 38610.4
Shell Scripts (8 concurrent) 32570.5 32458.8
System Call Overhead 2607.4 2672.7
======== ========
System Benchmarks Index Score 11077.2 11393.5
Changes from v1->v2:
-Removed preemption disable in the busy wait loop
-Changed busy spin condition to TASK_RUNNING state of the current thread
-Added usr+sys time for hackbench runs as shown by time command
subhra mazumdar (1):
pipe: busy wait for pipe
fs/pipe.c | 12 ++++++++++++
include/linux/pipe_fs_i.h | 2 ++
kernel/sysctl.c | 7 +++++++
3 files changed, 21 insertions(+)
--
2.9.3
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