linux-kernel - Re: [PATCH 1/5] asm-generic: add smp_vcond_load

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Message-ID: <2306e1b324c135d7d2bf961202657031d02ad4b0.camel@amazon.com>
Date: Wed, 6 Nov 2024 17:06:53 +0000
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Subject: Re: [PATCH 1/5] asm-generic: add smp_vcond_load_relaxed()

On Tue, 2024-11-05 at 11:36 -0800, Christoph Lameter (Ampere) wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> On Tue, 5 Nov 2024, Haris Okanovic wrote:
> 
> > +/**
> > + * smp_vcond_load_relaxed() - (Spin) wait until an expected value at address
> > + * with no ordering guarantees. Spins until `(*addr & mask) == val` or
> > + * `nsecs` elapse, and returns the last observed `*addr` value.
> > + *
> > + * @nsecs: timeout in nanoseconds
> 
> Please use an absolute time in nsecs instead of a timeout.

I went with relative time because it clock agnostic. I agree deadline
is nicer because it can propagate down layers of functions, but it pins
the caller to single time base.

> You do not know
> what will happen to your execution thread until the local_clock_noinstr()
> is run.


Not sure what you mean. Could you perhaps give an example where it
would break?

> 
> 

One alternative is to do timekeeping with delay() in all cases, to
decouple from sched/clock.