Date: Thu, 17 Jul 2008 08:57:13 -0400 From: John Baldwin <jhb@freebsd.org> To: Scott Long <scottl@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/dev/ciss ciss.c cissio.h cissreg.h cissvar.h Message-ID: <200807170857.13575.jhb@freebsd.org> In-Reply-To: <200807112121.m6BLL70t031426@repoman.freebsd.org> References: <200807112121.m6BLL70t031426@repoman.freebsd.org>
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On Friday 11 July 2008 05:20:51 pm Scott Long wrote: > scottl 2008-07-11 21:20:51 UTC > > FreeBSD src repository > > Modified files: > sys/dev/ciss ciss.c cissio.h cissreg.h cissvar.h > Log: > SVN rev 180454 on 2008-07-11 21:20:51Z by scottl > > A number of significant enhancements to the ciss driver: > > 3. Implemented MSI-X. Without any docs on this, I was just taking a > guess, and it appears to only work with the Performant method. This > could be a programming or understanding mistake on my part. While this > by itself made almost no difference to performance since the Performant > method already eliminated most of the synchronous reads over the PCI > bus, it did allow the CISS hardware to stop sharing its interrupt with > the USB hardware, which in turn allowed the driver to become decoupled > from the Giant-locked USB driver stack. This increased performance by > almost 20%. The MSI-X setup was done with 4 vectors allocated, but only > 1 vector used since the performant method was told to only use 1 of 4 > queues. Fiddling with this might make it work with the simpleq method, > not sure. I did not implement MSI since I have no MSI-specific hardware > in my test lab. One note here is that since you only use 1 message currently, you should really only alloc 1 message. That is: val = pci_msix_count(dev); if (val != CISS_MSI_COUNT) return (ENXIO); /* Currently only a single message is used. */ val = 1; error = pci_alloc_msix(dev, &val); ... The reason being that this "plays nicer" as far as system resource are concerned (only reserves 1 IDT slot vs 4 on x86 for example). In the case of MSI-X it also results in the same exact register updates since for MSI-X the count is never set in the config registers, instead we adjust each table entry during bus_setup_intr(). -- John Baldwin
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