Date: Thu, 18 Nov 1999 00:28:42 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Charles Randall <crandall@matchlogic.com> Cc: freebsd-smp@FreeBSD.ORG Subject: Re: RE: Big Giant Lock progress? Message-ID: <199911180828.AAA79093@apollo.backplane.com> References: <64003B21ECCAD11185C500805F31EC0304621F4F@houston.matchlogic.com>
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:From: Matthew Dillon [mailto:dillon@apollo.backplane.com]
:> Alfred got caught up in real life work so it's been on hold for a while.
:
:Has anyone profiled an SMP kernel in a standard role (Web server, NFS
:server, development machine, etc) and compared the points of BGL contention
:with the ease (or difficulty) of more fine-grained locking in those areas?
:
:In other words, have the "bang for the buck" areas been identified?
:
:Charles
There are three major areas of interest:
* parallelizing within the network stack
* parallelizing network interrupts and the
network stack
* parallelizing the cached read/write data
path, so the supervisor can copy data
to user processes on several cpu's at
once.
A whole lot of groundwork needs to happen before
we can do any of this stuff, though. A previous
attempt to optimizing just #3 in uiomove did not
produce very good results, mainly oweing to the
bgl being held too long in other places.
There are also some neat optimizations that
can be done, especially with the simplelocks.
For example, when unlocking a simplelock you do
not need to used a locked instruction or even
a cmpexg instruction, because you already own
the lock and nobody else can mess with it.
Nor do you need to use a locked assembly instruction
when bumping the ref count on a simplelock you
already hold. I think I am going to commit those even
without Alfred's work, once I separate them out
and have a little time, because they at least double
the speed of the simplelocks.
-Matt
Matthew Dillon
<dillon@backplane.com>
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