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From Richard Gooch <>
Subject Re: /dev/poll vs. aio_ (was: Re: Proposal: Get rid of most accept mutex)calls on hybrid server.)
Date Sat, 29 May 1999 02:00:57 GMT
Stephen C. Tweedie writes:
> Hi,
> On Sat, 29 May 1999 07:51:25 +1000, Richard Gooch <> said:
> > Why not just increase the RT signal queue size? Add a command to
> > prctl(2) so the application can tune this.
> Letting the application increase the queue size opens up a DOS attack:
> you can lock down arbitrarily much non-swappable memory with it.  root
> can already tune it via /proc/sys/kernel/rtsig-max.

OK, so there's a way for the administrator to tune this. I note the
default on my system is 1024, which should be fine for most
applications. However, for a busy WWW server, how deep should the
queue be? Anyone got a benchmark?

Assuming you need a much deeper queue (4096 for example), then tuning
rtsig-max will work, but at the cost of increasing the queue depth for
all processes, most of which won't need it. So how about creating
rtsig-limit and adding a command to prctl(2), so that a process which
needs to increase the queue depth can do so (up to the sysadmin tuned
limit), but other processes use the default?



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