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List:       varnish-misc
Subject:    how small can I make the thread stack size?
From:       kb+varnish () slide ! com (Ken Brownfield)
Date:       2010-07-28 13:39:54
Message-ID: AD13371D-FDE3-4F24-8ECB-7E02F71C750A () slide ! com
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+1.  256k was as low as I could safely go on x86_64, but it's been stable.

I used the ulimit hack for a bit, and it worked fine.

The official patch only controls workers, but the patch below will extend the control \
to the backend threads, which also scale with load.  If you aren't already building \
                varnish from source, the ulimit trick is probably just fine.
-- 
Ken

--- bin/varnishd/cache_backend_poll.c.orig	2009-04-01 06:35:15.000000000 -0700
+++ bin/varnishd/cache_backend_poll.c	2009-07-27 13:23:55.000000000 -0700
@@ -406,6 +414,7 @@
 {
 	struct vbp_target *vt;
 	struct vsb *vsb;
+	pthread_attr_t be_attr;
 
 	ASSERT_CLI();
 
@@ -444,7 +453,15 @@
 
 	VTAILQ_INSERT_TAIL(&vbp_list, vt, list);
 
-	AZ(pthread_create(&vt->thread, NULL, vbp_wrk_poll_backend, vt));
+	/* Set the stacksize for backend threads */
+	pthread_attr_init(&be_attr);
+	if (params->wthread_stacksize) {
+		int pt_res = pthread_attr_setstacksize(&be_attr, params->wthread_stacksize);
+		VSL(SLT_Debug, 0, "Attempt to set backend thread stacksize to %u %s",
+		    params->wthread_stacksize, pt_res ? "FAILED" : "succeeded");
+	}
+
+	AZ(pthread_create(&vt->thread, &be_attr, vbp_wrk_poll_backend, vt));
 }
 
 void


On Jul 28, 2010, at 2:24 AM, Chris Hecker wrote:

> 
> Alright, I'll try 256kb and see how it goes.  I'm doing it with a config param to \
> varnishd, which unfortunately makes it still use 10mb stacks for the other 6 \
> threads it's running.  I wonder if I should use ulimit in the init script to avoid \
> this and save 60mb... 
> Thanks,
> Chris
> 
> 
> On 2010/07/28 01:29, Cosimo Streppone wrote:
> > On Wed, 28 Jul 2010 08:02:50 +0200, Chris Hecker <checker at d6.com> wrote:
> > 
> > > [stack size] I've seen people talking about 256kb, but then the docs
> > > are pretty sketchy on whether it's a good idea to change it at all,
> > > Any advice?
> > 
> > We're running several varnish instances.
> > All of them x86-64 though, so YMMV.
> > 
> > For the busiest machines, stack size has been set to 256kb, by putting
> > 'ulimit -s 256' in the init script.
> > 
> > IIRC, we started doing this because we saw increases in the
> > 'thread_limited'
> > counter.
> > We saw that varnishd couldn't create new threads,
> > even if the hard limit (thread_pool_max) hadn't been reached yet.
> > Check:
> > 
> > http://lists.varnish-cache.org/pipermail/varnish-misc/2009-August/002977.html
> > 
> > 
> > These particular instances are constantly running 7k threads,
> > occasionally going to 8-9k. With 24 Gb of RAM.
> > 


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