Date: Tue, 13 Jul 2021 14:27:46 -0600 From: Warner Losh <imp@bsdimp.com> To: Hans Petter Selasky <hps@selasky.org> Cc: Gary Jennejohn <gljennjohn@gmail.com>, "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net>, Michael Gmelin <freebsd@grem.de>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: Killing Giant for 13 Message-ID: <CANCZdfrOg76REnzp=gR3zDy7f3uM8p6nE4nih1-EmGb0AbpSmg@mail.gmail.com> In-Reply-To: <d0105f03-73fe-1e8f-0fbe-8c180f2679a6@selasky.org> References: <CANCZdfr0CpDBQ6QWJ_CTtOLW6EwAke_Vr_imqa5=GBzRAoa6eA@mail.gmail.com> <201911260917.xAQ9Hcf1001914@gndrsh.dnsmgr.net> <CANCZdfowGPBgp14aaJ15GnYOkRb_C91AeRqFY-axqu%2BCOScz8w@mail.gmail.com> <20191126193555.047a63cf@bsd64.grem.de> <20191126194750.3ff939c3@ernst.home> <CANCZdfoOXXd88kaJtkHfkfmdCkv2WnoXZBNedjyEOb8jxGK==A@mail.gmail.com> <20191127082615.7c59857c@ernst.home> <d0105f03-73fe-1e8f-0fbe-8c180f2679a6@selasky.org>
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--000000000000cad85405c70712e3 Content-Type: text/plain; charset="UTF-8" On Tue, Jul 13, 2021 at 9:13 AM Hans Petter Selasky <hps@selasky.org> wrote: > Hi, > > I've been pondering with some ideas around Giant removal too. > > First of all, I think the first step getting rid of Giant, is to move > all Giant usage related to newbus into two own global functions, so we > can start working on what and how the device tree should be protected > separately. Personally I would prefer a sleepable EPOCH (See > https://reviews.freebsd.org/D30376), because that would interact nicely > with freeing the device softc and other internal structures. > Yea, I'm unsure of epoch or smr is the right path forward here, but at a high level, I'm thinking along the same lines as you are. > void > device_tree_lock() > { > mtx_lock(&Giant); > } > > void > device_tree_unlock() > { > mtx_unlock(&Giant); > } > I have a tree with this change worked through already, though with a different name. I've also pushed Giant down a bit in a few places too in that tree. > Secondly I think that if we can remove all code sleeping with Giant, so > to speak, either by using msleep(&Giant) or by using M_NOWAIT, we can > get rid of the DROP and PICKUP Giant macros, and get Giant out of the > fast path in all of the kernel. Then if Giant i still around as a mutex, > it won't have that much impact! > > Warner, what is the status of your Giant work? > Stalled a bit for want of time, and waiting on the big ball of goo that's the x86 keyboard / console driver to reach some kind of resolution. I posted https://reviews.freebsd.org/D23388 a while back, but got bogged down removing the Giant requirement from device_busy because there's a few infrequently used drivers that are tricky to test that are using it. https://reviews.freebsd.org/D26284 has the code to do that, but I think I got distracted by the quiesce discussion which is a better way to cope, but again, involves a number of infrequently used drivers. Both of these reviews likely needs to be rebased, if I don't happen to have them in a local git branch (they date from the dawn of my git svn usage, so maybe got dropped along the way by mistake). Warner --000000000000cad85405c70712e3--
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