Re: [PATCH v0.9.1 0/6] sched,mm,x86/uaccess: implement User Managed Concurrency Groups

From: Peter Zijlstra <peterz@infradead.org>
To: Peter Oskolkov <posk@posk.io>
Cc: Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-api@vger.kernel.org, Paul Turner <pjt@google.com>,
	Ben Segall <bsegall@google.com>, Peter Oskolkov <posk@google.com>,
	Andrei Vagin <avagin@google.com>, Jann Horn <jannh@google.com>,
	Thierry Delisle <tdelisle@uwaterloo.ca>
Subject: Re: [PATCH v0.9.1 0/6] sched,mm,x86/uaccess: implement User Managed Concurrency Groups
Date: Wed, 24 Nov 2021 18:20:18 +0100	[thread overview]
Message-ID: <YZ50UoNxtsACynjZ@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAFTs51Vp=hfiDkSHVysHLh9QOqpUXUksF-SW86GOd5ih-=7JPQ@mail.gmail.com>

On Wed, Nov 24, 2021 at 08:28:43AM -0800, Peter Oskolkov wrote:
> On Wed, Nov 24, 2021 at 6:06 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, Nov 22, 2021 at 01:13:21PM -0800, Peter Oskolkov wrote:
> > > User Managed Concurrency Groups (UMCG) is an M:N threading
> > > subsystem/toolkit that lets user space application developers implement
> > > in-process user space schedulers.
> > >
> > > This v0.9.1 patchset is the same as v0.9, where u32/u64 in
> > > uapi/linux/umcg.h are replaced with __u32/__u64, as test robot/lkp
> > > does not recognize u32/u64 for some reason.
> > >
> > > v0.9 is v0.8 rebased on top of the current tip/sched/core,
> > > with a fix in umcg_update_state of an issue reported by Tao Zhou.
> > >
> > > Key changes from patchset v0.7:
> > > https://lore.kernel.org/all/20211012232522.714898-1-posk@google.com/:
> > >
> > > - added libumcg tools/lib/umcg;
> > > - worker "wakeup" is reworked so that it is now purely a userspace op,
> > >   instead of waking the thread in order for it to block on return
> > >   to the userspace immediately;
> > > - a couple of minor fixes and refactorings.
> > >
> > > These big things remain to be addressed (in no particular order):
> > > - support tracing/debugging
> > > - make context switches faster (see umcg_do_context_switch in umcg.c)
> > > - support other architectures
> > > - cleanup and post selftests in tools/testing/selftests/umcg/
> > > - allow cross-mm wakeups (securely)
> >
> > *groan*... so these patches do *NOT* support the very thing this all
> > started with, namely block + wakeup notifications. I'm really not sure
> > how that happened, as that was the sole purpose of the exercise.
> 
> I'm not sure why you say this - in-process block/wakeup is very much
> supported - please see the third patch. Cross-process (cross-mm)
> wakeups are not supported at the moment, as the security story has to
> be fleshed out.

I seem to have gotten submit and update work confused. I'll go stare
more. For some reason I find it very hard to read this stuff.