On Dec 26, 2008, at 18:33, Scott Long <sco...@samsco.org> wrote:
On Dec 26, 2008, at 5:38 PM, Alfred Perlstein <alf...@freebsd.org>
wrote:
* M. Warner Losh <i...@bsdimp.com> [081216 11:06] wrote:
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...
Easy enough to stash a "once" varible in the generic device struct
and warn when returning from an isr when INVARIANTS or something is
turned on.
Then you'd only get one warning per device once it happens.
I prefer to do nothing. It's not unsafe or erroneous to access cfg
registers. But if some kind of message does get added, I insist
that it drop all pretenses and say, "you're too poor to run freebsd,
come back when you can afford better hardware.". :)
Scott
Unfortunately embedded systems can't win the lottery ;.).
-Garrett
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