Date: Tue, 16 Dec 2008 12:04:12 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: scottl@samsco.org Cc: svn-src-head@FreeBSD.org, mav@FreeBSD.org, src-committers@FreeBSD.org, svn-src-all@FreeBSD.org Subject: Re: svn commit: r186182 - head/sys/dev/ata Message-ID: <20081216.120412.1346820326.imp@bsdimp.com> In-Reply-To: <4947F363.4010909@samsco.org> References: <4947D474.9040802@samsco.org> <20081216.101038.1172765453.imp@bsdimp.com> <4947F363.4010909@samsco.org>
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In message: <4947F363.4010909@samsco.org>
Scott Long <scottl@samsco.org> writes:
: M. Warner Losh wrote:
: > In message: <4947D474.9040802@samsco.org>
: > Scott Long <scottl@samsco.org> writes:
: > : Alexander Motin wrote:
: > : > Author: mav
: > : > Date: Tue Dec 16 16:04:40 2008
: > : > New Revision: 186182
: > : > URL: http://svn.freebsd.org/changeset/base/186182
: > : >
: > : > Log:
: > : > Call ata_legacy() only once on attach and save it's result. Scanning PCI
: > : > configuration registers (which are not going to change) on every interrupt
: > : > looks expensive, especially when interrupt is shared. Profiling shows me 3%
: > : > of time spent by atapci0 on pure network load due to IRQ sharing with em0.
: > : >
: > :
: > : Nice change. PCI Config registers are exceptionally slow to access on
: > : most systems.
: >
: > And we've been recommending to people for years that they avoid config
: > space access in interrupt handlers. Maybe it is time for something
: > that checks and prints a warning?
: >
:
: With the move to memory-mapped pci config registers, there was an
: intention to allow low-end devices to put their registers into config
: space. I think I recall some legacy ultra-low end devices that also
: put a few required registers into config space. So while it's not ideal
: to access it from an interrupt handler, I can't think of why it should
: be expressly forbidden.
True. I wasn't planning on banning it, just warning about it so we
could be purposeful in our use of it. Likely unworkable though...
Warner
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