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author | Miklos Szeredi <mszeredi@suse.cz> | 2009-03-23 16:07:24 +0100 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-03-23 09:22:31 -0700 |
commit | 53da1d9456fe7f87a920a78fdbdcf1225d197cb7 (patch) | |
tree | eccd5357ceff25a9a07be802ac0161c8c1842e64 /arch/sparc/kernel/kgdb_64.c | |
parent | b0dcb4a91ddb79f2e213205cf8d86b467f8559c7 (diff) |
fix ptrace slowness
This patch fixes bug #12208:
Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=12208
Subject : uml is very slow on 2.6.28 host
This turned out to be not a scheduler regression, but an already
existing problem in ptrace being triggered by subtle scheduler
changes.
The problem is this:
- task A is ptracing task B
- task B stops on a trace event
- task A is woken up and preempts task B
- task A calls ptrace on task B, which does ptrace_check_attach()
- this calls wait_task_inactive(), which sees that task B is still on the runq
- task A goes to sleep for a jiffy
- ...
Since UML does lots of the above sequences, those jiffies quickly add
up to make it slow as hell.
This patch solves this by not rescheduling in read_unlock() after
ptrace_stop() has woken up the tracer.
Thanks to Oleg Nesterov and Ingo Molnar for the feedback.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/sparc/kernel/kgdb_64.c')
0 files changed, 0 insertions, 0 deletions