linux-kernel - Re: [PATCH net-next 3/3] ptp: idt82p33: optimize _idt82p33

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Date:   Thu, 5 Nov 2020 09:02:04 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     min.li.xe@...esas.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 3/3] ptp: idt82p33: optimize _idt82p33_adjfine

On Thu, Nov 05, 2020 at 02:35:56AM +0200, Vladimir Oltean wrote:
> On the other hand and with all due respect, saying that it may have been
> 'buggy on some archs back in the day' and then not bringing any evidence
> is a bit of a strange claim to make.

You're right.  I made the effort to look back into the days of v3.0,
and the only thing I could find is that the 32 bit implementation of
div_s64 does extra operations and invokes an additional function call.
But the difference in performance, if any, is probably not very large.

> I am actively using div_s64 in drivers/net/dsa/sja1105/sja1105_ptp.c
> successfully on arm and arm64.

Yeah, I see div_s64 has found its way into the ntp code, too, so it
must be fine.

Thanks,
Richard