Worker thread stack size

[Poul-Henning Kamp]

I have added a parameter to set the worker thread stack size.

I suspect we can get away with something as low as maybe 64k +
$sess_workspace, but I have absolutely no data to confirm or
deny this claim.

If a couple of you could spend a few minutes to examine actual
stack sizes and report back, that would be nice.

The number I am interested in, is the number of mapped and
modified pages in the worker-thread stacks.

On FreeBSD, the mincore(2) could report this, but on Linix mincore(2)
only reports mapped vs. unmapped pages, which may or may not be
enough.  In either case, it would require some hackish code in Varnish.

A better way is to ask your systems VM system, for instance by
looking at /proc/$pid/map.

On a 64bit FreeBSD system, the entries you are looking for look like
this:
	0x7ffffddd0000 0x7ffffddf0000 3 0 0xffffff003d87e0d8 rw- 1 0 0x3100 NCOW NNC default - CH 488
	0x7ffffdfd1000 0x7ffffdff1000 3 0 0xffffff0028845d80 rw- 1 0 0x3100 NCOW NNC default - CH 488
	0x7ffffe1d2000 0x7ffffe1f2000 3 0 0xffffff00635eea20 rw- 1 0 0x3100 NCOW NNC default - CH 488
	0x7ffffe3d3000 0x7ffffe3f3000 3 0 0xffffff0095d57870 rw- 1 0 0x3100 NCOW NNC default - CH 488
	0x7ffffe5d4000 0x7ffffe5f4000 3 0 0xffffff00630ec0d8 rw- 1 0 0x3100 NCOW NNC default - CH 488

And the number I need is the difference between the first two colums
for all your worker threads, (min, max, average accepted also )
and the value of your sess_workspace parameter.

In the case you would find:
	0x7ffffddf0000 - 0x7ffffddd0000 = 128K
	0x7ffffdff1000 - 0x7ffffdfd1000 = 128K
	...

Poul-Henning


In message <20091118123439.6A18C38D0D at projects.linpro.no>, phk at projects.linpro.
no writes:
>Author: phk
>Date: 2009-11-18 13:34:39 +0100 (Wed, 18 Nov 2009)
>New Revision: 4352
>
>Modified:
>   trunk/varnish-cache/bin/varnishd/cache_pool.c
>   trunk/varnish-cache/bin/varnishd/heritage.h
>   trunk/varnish-cache/bin/varnishd/mgt_pool.c
>Log:
>Add a parameter to set the workerthread stacksize.
>
>On 32 bit systems, it may be necessary to tweak this down to get high
>numbers of worker threads squeezed into the address-space.
>
>I have no idea how much stack-space a worker thread normally uses, so
>no guidance is given, and we default to the system default.
>
>Fixes #572

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.