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>
next in thread | previous in thread | raw e-mail | index | archive | help
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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20081216.120412.1346820326.imp>