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Re: [Discuss-gnuradio] Flarging big FFTs
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] Flarging big FFTs |
Date: |
Fri, 23 Jan 2009 10:19:14 -0800 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Fri, Jan 23, 2009 at 01:01:24PM -0500, Marcus D. Leech wrote:
> I can't use FFTs larger than about 180000 bins without getting "shared
> memory allocation" errors in Gnu Radio.
>
> Is there an easy fix for this?
>
> For SETI work, being able to (for example) compute an 8 million point
> FFT for an 8Msps signal gives you 1Hz
> resolution. But I can't seem to get anywhere near this without the
> allocator griping at me.
>
Hi Marcus,
You need to bump up the shared memory maximum segment size.
You can do this with the sysctl command. On some systems there's also
an /etc/sysctl.conf file. The defaults appear to depend on your
distribution. The parameter you want to increase is kernel.shmmax.
address@hidden trunk]$ sudo sysctl -a | grep shm
kernel.shmmax = 268435456
kernel.shmall = 2097152
kernel.shmmni = 4096
vm.hugetlb_shm_group = 0
The output above is from an x86 Fedora 9 system. It's pretty big by default.
See also
$ man sysctl
$ man sysctl.conf
http://bugzilla.kernel.org/show_bug.cgi?id=11381
Eric