CVS commit: src/sys/dev/pci

["SAITOH Masanobu" <msaitoh%netbsd.org@localhost>]

Module Name:    src
Committed By:   msaitoh
Date:           Wed Mar 27 03:29:50 UTC 2019

Modified Files:
        src/sys/dev/pci: if_bnx.c

Log Message:
 Apply OpenBSD rev. 1.94:

 > ido not disable interrupts in the isr and then enable them again
 > when leaving. when you're handling an interrupt it is masked.
 > whacking the chip is work for no gain.
 >
 > modify the interrupt handler so it only processes the rings once
 > rather than looping over them until it runs out of work to do
 >
 > looping in the isr is bad for several reasons:
 >
 > firstly, the chip does interrupt mitigation so you have a
 > decent/predictable amount of work to do in the isr. your first loop
 > will do that chunk of work (ie, it pulls off 50ish packets), and
 > then the successive looping aggressively pull one or two packets
 > off the rx ring. these extra loops work against the benefit that
 > interrupt mitigation provides.
 >
 > bus space reads are slow. we should avoid doing them where possible
 > (but we should always do them when necessary).
 >
 > doing the loop 5 times per isr works against the mclgeti semantics.
 > it knows a nic is busy and therefore needs more rx descriptors by
 > watching to see when the nic uses all of its descriptors between
 > interrupts. if we're aggressively pulling packets off by looping
 > in the isr then we're skewing this check.
 >
 > ok deraadt@


To generate a diff of this commit:
cvs rdiff -u -r1.69 -r1.70 src/sys/dev/pci/if_bnx.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.