Date: Wed, 13 Jan 2021 11:42:22 GMT From: myfreeweb <greg@unrelenting.technology> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Emmanuel Vadot <manu@freebsd.org>, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 11d62b6f31ab - main - linuxkpi: add kernel_fpu_begin/kernel_fpu_end Message-ID: <A7AF80F3-3E01-44DD-B1FF-49BAEFCF4C4A@unrelenting.technology> In-Reply-To: <20210113110826.46fbc900b3c375e7215a8195@bidouilliste.com> References: <202101121143.10CBh02x095972@gitrepo.freebsd.org> <X/2hR9Hi3Jhf5ZNs@kib.kiev.ua> <20210113110826.46fbc900b3c375e7215a8195@bidouilliste.com>
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On January 13, 2021 10:08:26 AM UTC, Emmanuel Vadot <manu@bidouilliste=2Ec= om> wrote: >On Tue, 12 Jan 2021 15:16:55 +0200 >Konstantin Belousov <kostikbel@gmail=2Ecom> wrote: > >> On Tue, Jan 12, 2021 at 11:43:00AM +0000, Emmanuel Vadot wrote: >> > The branch main has been updated by manu: >> >=20 >> > URL: https://cgit=2EFreeBSD=2Eorg/src/commit/?id=3D11d62b6f31ab4e99df= 6d0c6c23406b57eaa37f41 >> >=20 >> > commit 11d62b6f31ab4e99df6d0c6c23406b57eaa37f41 >> > Author: Emmanuel Vadot <manu@FreeBSD=2Eorg> >> > AuthorDate: 2021-01-12 11:02:38 +0000 >> > Commit: Emmanuel Vadot <manu@FreeBSD=2Eorg> >> > CommitDate: 2021-01-12 11:31:00 +0000 >> >=20 >> > linuxkpi: add kernel_fpu_begin/kernel_fpu_end >> > =20 >> > With newer AMD GPUs (>=3DNavi,Renoir) there is FPU context usage = in the >> > amdgpu driver=2E >> > The `kernel_fpu_begin/end` implementations in drm did not even al= low nested >> > begin-end blocks=2E >>=20 >> Does Linux allow more then one thread to execute kernel_fpu_begin ? > > I actually have no idea, adding Greg to cc=2E Looks like they save the context into the current thread state, so yes? (d= rm doesn't need that) Also they seem to do something FPU_KERN_NOCTX like (??) because they disab= le preemption inside these blocks=2E (Where does our NOCTX actually store the state?) Apparently the API shouldn't actually support nesting these sections, beca= use kernel_fpu_end unconditionally enables preemption=2E But that nesting w= ould not just panic like it did on our old impl=2E (Indeed in newest linux = versions there's a WARN on nesting =E2=80=93 only a warning though, not a p= anic!) And amdgpu relies on that not panicking=2E Looks like amdgpu will narrow the FPU sections down now, they are struggli= ng with FPU stuff upstream too: https://www=2Espinics=2Enet/lists/kernel/msg3793776=2Ehtml
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