In message: <4947f363.4010...@samsco.org>
Scott Long <sco...@samsco.org> writes:
: M. Warner Losh wrote:
: > In message: <4947d474.9040...@samsco.org>
: > Scott Long <sco...@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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