Date: Thu, 21 Oct 2004 13:43:35 -0700 (PDT) From: Jason Stone <freebsd-performance@dfmm.org> To: freebsd-performance@freebsd.org Cc: luigi@iet.unipi.it Subject: Re: decreasing interrupt CPU load Message-ID: <20041021133719.S79820@walter> In-Reply-To: <0A85B89D-2369-11D9-BD7C-000A95EFF4CA@foolishgames.com> References: <20041020133406.V79820@walter> <0A85B89D-2369-11D9-BD7C-000A95EFF4CA@foolishgames.com>
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > If you look at http://info.iet.unipi.it/~luigi/polling, the last Q & A > question suggests why it is disabled for SMP. It seems that polling > only runs on one thread whereas an smp box might handle concurrently > interupts from different devices. > > Can the scheduler move the thread to another cpu or is it locked on a > particular cpu? thanks for the pointer. it seems to me that the thread doing the polling could move from cpu to cpu, but that's not the issue - the issue, if I'm understanding the author, is that the polling thread will always be a single thread, whereas if we use traditional interrupts, they can be handled on multiple cpu's concurrently. so interrupts, with multiple cpu's to handle them, might give much better performance than a single polling thread. if that's the only issue, then preventing one from compiling with both SMP and DEVICE_POLLING doesn't seem necesary, since you can turn polling on and off at runtime with sysctl's. luigi: does that sound right to you? has any consideration been giving to removing the restriction preventing DEVICE_POLLING from building on an SMP system, in light of the fact that polling can just be turned off if it's giving suboptimal performance? -Jason -------------------------------------------------------------------------- Freud himself was a bit of a cold fish, and one cannot avoid the suspicion that he was insufficiently fondled when he was an infant. -- Ashley Montagu -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (FreeBSD) Comment: See https://private.idealab.com/public/jason/jason.gpg iD8DBQFBeB95swXMWWtptckRAvlRAJ4806zyUOwMq89qgNKXlbbOE826LQCg6AGW qWDj3u/F4V3a51YJQAA2qpM= =sN26 -----END PGP SIGNATURE-----
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