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definitions=main-2311090163 X-Proofpoint-ORIG-GUID: l-JqCpufFQ7kHTapdNk2pv5tlKjJWSwT X-Proofpoint-GUID: l-JqCpufFQ7kHTapdNk2pv5tlKjJWSwT X-Rspam-User: X-Stat-Signature: 51g76tb3tb67tubdy6yzqwdx5hn7yqte X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4C87C4000D X-HE-Tag: 1699568901-229640 X-HE-Meta: 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 VDCXOHmY 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on the runqueue, this just >> amounts to spinning in a tight-loop with a cond_resched(). >> (When running in a fully preemptible kernel, cond_resched() >> calls are stubbed out so it amounts to even less.) >> >> In sum, cond_resched() in error handling/retry contexts might >> be useful in avoiding softlockup splats, but not very good at >> error handling. Ideally, these should be replaced with some kind >> of timed or event wait. >> >> For now add cond_resched_stall(), which tries to schedule if >> possible, and failing that executes a cpu_relax(). > > What's the point of this new variant of cond_resched()? We really do not > want it at all. > >> +int __cond_resched_stall(void) >> +{ >> + if (tif_need_resched(RESCHED_eager)) { >> + __preempt_schedule(); > > Under the new model TIF_NEED_RESCHED is going to reschedule if the > preemption counter goes to zero. Yes agreed. cond_resched_stall() was just meant to be window dressing. > So the typical > > while (readl(mmio) & BUSY) > cpu_relax(); > > will just be preempted like any other loop, no? Yeah. But drivers could be using that right now as well. I suspect people don't like the idea of spinning in a loop and, that's why they use cond_resched(). Which in loops like this, is pretty much: while (readl(mmio) & BUSY) ; The reason I added cond_resched_stall() was as an analogue to cond_resched_lock() etc. Here, explicitly giving up CPU. Though, someone pointed out a much better interface to do that sort of thing: readb_poll_timeout(). Not all but a fair number of sites could be converted to that. Ankur