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definitions=main-2311090164 X-Proofpoint-GUID: 225g_zMv69bIZ7a4hh_W6NHeSUAbxeYz X-Proofpoint-ORIG-GUID: 225g_zMv69bIZ7a4hh_W6NHeSUAbxeYz X-Rspamd-Queue-Id: 09B33180018 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 9bwr14kouubkyr57sd6g9mdtpfsgee8f X-HE-Tag: 1699569427-221942 X-HE-Meta: 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 83KIZ6Rw fRX2qkW/L2qe+QAj4ITClHg/R103q40VF7sfIKLp2q17fQ86/acFS7SnqfEBZURJHd2LDAEOA9GiuK+prpU/r+f6Qmu4+ybZItacU8Rnh5P+SKaAY029Z/4tpY4Dcr696CUx52zXxOIHvblU+fvtstQ+pL41JZsbzhr5R8udtoLmaeXAZ/kyUfrwzowHoTSFeVcyiyrPw9ipsohBoy4NIXC0discQOMfOB3DiWddnbW49q0IqR+/zEUIW4U2hUnTSL6JSID8vsqhIzM3jxXimJYV16Cf+2q3qLd0vRKmn3B7OdsnXGBxkXC28FAQ8DsRmV4aE/LiNMIBJAup0dDWvqxzsBnkTa9ncWfdBW8Pa+7I86LwTShcEEzdzslEV3wt0gZq4Y6gH7lK3p+l/Bwth7s9tUVOY3yx+aJKI X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Mark Rutland writes: > On Wed, Nov 08, 2023 at 04:34:41PM -0800, Ankur Arora wrote: >> Mark Rutland writes: >> >> > On Tue, Nov 07, 2023 at 01:56:46PM -0800, Ankur Arora wrote: >> >> What's broken: >> >> - ARCH_NO_PREEMPT (See patch-45 "preempt: ARCH_NO_PREEMPT only preempts >> >> lazily") >> >> - Non-x86 architectures. It's trivial to support other archs (only need >> >> to add TIF_NEED_RESCHED_LAZY) but wanted to hold off until I got some >> >> comments on the series. >> >> (From some testing on arm64, didn't find any surprises.) >> > >> > When you say "testing on arm64, didn't find any surprises", I assume you mean >> > with an additional patch adding TIF_NEED_RESCHED_LAZY? >> >> Yeah. And, handling that in the user exit path. >> >> > Note that since arm64 doesn't use the generic entry code, that also requires >> > changes to arm64_preempt_schedule_irq() in arch/arm64/kernel/entry-common.c, to >> > handle TIF_NEED_RESCHED_LAZY. >> >> So, the intent (which got muddied due to this overly large series) >> was to delay handling TIF_NEED_RESCHED_LAZY until we are about to >> return to user. > > Ah, I missed that detail -- thanks for clarifying! > >> I think arm64_preempt_schedule_irq() should only handle TIF_NEED_RESCHED >> and the _TIF_NEED_RESCHED_LAZY should be handled via _TIF_WORK_MASK >> and do_notify_resume(). > > Digging a bit more, I think that should still work. > > One slight clarification: arm64_preempt_schedule_irq() doesn't look at > TIF_NEED_RESCHED today, as it relies on the scheduler IPI calling > preempt_fold_need_resched() to propogate TIF_NEED_RESCHED into > PREEMPT_NEED_RESCHED. That should still work since this series makes > preempt_fold_need_resched() check tif_need_resched(RESCHED_eager). > > I was a bit cnofused because in the generic entry code, > irqentry_exit_cond_resched() explicitly checks for TIF_NEED_RESCHED, and I'm > not sure why it does that rather than relying on the scheduler IPI as above. Yeah I found that confusing as well. I suspect the reason is that not all archs do the folding and we need the explicit check for those that don't. -- ankur