Re: ps performance sucks (was Re: dcache_rcu [performance results])

[jw schultz]

On Mon, Nov 04, 2002 at 05:14:19PM -0800, Martin J. Bligh wrote:
> I think it's pretty trivial to make /proc/<pid>/psinfo, which
> dumps the garbage from all five files in one place. Which makes
> it 5 times better, but it still sucks.

And i'd still keep environ seperate.  I'm inclined to think
ps should never have presented it in the first place.
This is the direction i (for what it's worth) favor.

> > Don't get me wrong.  I believe in the one field per file
> > rule but ps &co are the exception that proves (tests) the
> > rule.  Especially on the heavily laden systems with
> > tens of thousands of tasks.  We could do with a something
> > between /dev/kmem and five files per pid.
> 
> I had a very brief think about this at the weekend, seeing
> if I could make a big melting pot /proc/psinfo file that did
> seqfile and read everything out in one go, using seq_file
> internally to interate over the tasklist. The most obvious
> problem that sprung to mind seems to be the tasklist locking -
> you obviously can't just hold a lock over the whole thing.
> As I know very little about that, I'll let someone else suggest
> how to do this, but I'm prepared to do the grunt work of implementing
> it if need be.

Yep, can't hold the lock across syscalls.  That would be
quite a bit of data to hold in a per fd buffer.  Think of
the big iron with tons of processes.

The other way i could see this working is to present it as a
sparse file.  ps (or whatever) would first get a list of
pids then iterate over them using lseek to set the file
offset to pid * CONSTANT_SIZE and read would return
something smaller than CONSTANT_SIZE bytes.  If the pid no
longer exists return 0.

I really hate this idea.  It stinks almost as much as
/dev/kmem.

-- 
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	J.W. Schultz            Pegasystems Technologies
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