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Date:   Tue, 13 Apr 2021 14:22:03 -0700
From:   Andi Kleen <ak@linux.intel.com>
To:     Alex Kogan <alex.kogan@oracle.com>
Cc:     linux@armlinux.org.uk, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, will.deacon@arm.com,
        arnd@arndb.de, longman@redhat.com, linux-arch@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, x86@kernel.org,
        guohanjun@huawei.com, jglauber@marvell.com,
        steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
        dave.dice@oracle.com
Subject: Re: [External] : Re: [PATCH v14 4/6] locking/qspinlock: Introduce
 starvation avoidance into CNA
Message-ID: <20210413212203.GT3762101@tassilo.jf.intel.com>
References: <20210401153156.1165900-1-alex.kogan@oracle.com>
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 <87mtu2vhzz.fsf@linux.intel.com>
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> > ms granularity seems very coarse grained for this. Surely
> > at some point of spinning you can afford a ktime_get? But ok.
> We are reading time when we are at the head of the (main) queue, but
> don’t have the lock yet. Not sure about the latency of ktime_get(), but
> anything reasonably fast but not necessarily precise should work.

Actually cpu_clock / sched_clock (see my other email). These should
be fast without corner cases and also monotonic.

> 
> > Could you turn that into a moduleparm which can be changed at runtime?
> > Would be strange to have to reboot just to play with this parameter
> Yes, good suggestion, thanks.
> 
> > This would also make the code a lot shorter I guess.
> So you don’t think we need the command-line parameter, just the module_param?

module_params can be changed at the command line too, so yes.

-Andi