Date: Mon, 14 Jan 2008 09:04:40 -0800 From: "Jordan Sissel" <psionic@gmail.com> To: "Kris Kennaway" <kris@freebsd.org>, current@freebsd.org, jls@freebsd.org Subject: Re: mpsafe psm driver needed Message-ID: <5ad23a300801140904w7da3a952m7d1b6cd45c2326e1@mail.gmail.com> In-Reply-To: <20080114110054.GK17508@fasolt.home.paeps.cx> References: <478A739F.2030003@FreeBSD.org> <20080114110054.GK17508@fasolt.home.paeps.cx>
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On Jan 14, 2008 3:00 AM, Philip Paeps <philip@freebsd.org> wrote: > On 2008-01-13 21:25:03 (+0100), Kris Kennaway <kris@FreeBSD.org> wrote: > > I've been looking at some mutex profiling traces from users of 6.x and 7.x > > who are reporting that their mouse pointer sometimes freezes when their > > system is busy. In most of the situations I have looked at this is because > > the psm driver is Giant-locked, and competes with other things like the > > syncer (in 6.x), or sysctl calls (I have a WIP for this that I need to > > revisit). > > > > This is a minor problem from a grand architectural point of view but an > > important one from a usability point of view. I believe these particular > > interactivity problems would be resolved if the psm driver no longer > > required Giant. Is anyone able to work on this? > > I have taken a look at this in the past. It's not a trivial problem. > > There is a lot of what I can only charitably call "legacy code" in psm and it > appears that as soon as you touch any of it, it upsets at least one brand of > KVM "out there". > > One of my mentees has been working on a rewrite for a while, but the project > has not yet been committed to cvs. > > jls: any news on this? > This was on my list of things to fix in psm(4) as part of the rewrite, but I haven't done that yet. Looks like it's become a priority now, so what better time? I must confess I don't have a great deal of experience with the freebsd kernel and its locking system. From what I can tell, the only outside resources psm(4) uses is spltty (which has been deprecated for some time, yes?), atkbdc, and giant. However, in searching the source, I see many instances of mtx_lock(&Giant), but none in psm.c. From looking at the code, it seems like if you pass D_NEEDGIANT in your flags when you call make_dev, some of your methods are implicitly wrapped with mutex locks which use Giant? (Forgive any oversight, it's 9am ;)) Any guidance is welcome regarding the best way to remove the need for giant. I'm happy to take on doing this, since I'm already somewhat familiar with psm(4). -Jordan > - Philip > > -- > Philip Paeps Please don't Cc me, I am > philip@freebsd.org subscribed to the list. > > It is impossible for an optimist to be pleasantly > suprised. > > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" >
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