Date: Sat, 2 Mar 2019 12:07:33 -0800 From: Mark Millard <marklmi@yahoo.com> To: Konstantin Belousov <kib@freebsd.org> Cc: Bruce Evans <brde@optusnet.com.au>, freebsd-hackers Hackers <freebsd-hackers@freebsd.org>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: powerpc64 head -r344018 stuck sleeping problems: th->th_scale * tc_delta(th) overflows unsigned 64 bits sometimes [patched failed] Message-ID: <EA4374C2-07F8-4D48-8D56-31B36295C389@yahoo.com> In-Reply-To: <87D6CBD5-AE55-4EC8-8797-D8A9DC3D5A5A@yahoo.com> References: <D3D7E9F4-9A5E-4320-B3C8-EC5CEF4A2764@yahoo.com> <20190228145542.GT2420@kib.kiev.ua> <20190228150811.GU2420@kib.kiev.ua> <962D78C3-65BE-40C1-BB50-A0088223C17B@yahoo.com> <28C2BB0A-3DAA-4D18-A317-49A8DD52778F@yahoo.com> <20190301112717.GW2420@kib.kiev.ua> <20190302043936.A4444@besplex.bde.org> <20190301194217.GB68879@kib.kiev.ua> <87D6CBD5-AE55-4EC8-8797-D8A9DC3D5A5A@yahoo.com>
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On 2019-Mar-1, at 13:19, Mark Millard <marklmi at yahoo.com> wrote:
> On 2019-Mar-1, at 11:42, Konstantin Belousov <kib at freebsd.org> wrote:
>
>> . . .
>> +#ifdef _LP64
>> + scale_bits = ffsl(scale);
>> +#else
>> + scale_bits = ffsll(scale);
>> +#endif. . .
>> + if (__predict_false(scale_bits + fls(delta) > 63)) {
>
>
> The patch from yesterday uniformly used:
>
> int
> fls(int mask)
> {
> int bit;
>
> if (mask == 0)
> return (0);
> for (bit = 1; mask != 1; bit++)
> mask = (unsigned int)mask >> 1;
> return (bit);
> }
>
> that looks for the most significant 1 bit.
>
> The new patch uses in some places:
>
> int
> ffsl(long mask)
> {
> int bit;
>
> if (mask == 0)
> return (0);
> for (bit = 1; !(mask & 1); bit++)
> mask = (unsigned long)mask >> 1;
> return (bit);
> }
>
> that looks for the least significant 1 bit. Similarly
> for:
>
> int
> ffsll(long long mask)
> {
> int bit;
>
> if (mask == 0)
> return (0);
> for (bit = 1; !(mask & 1); bit++)
> mask = (unsigned long long)mask >> 1;
> return (bit);
> }
>
> Was that deliberate?
Be that as it may:
I've been watching you and Bruce work on a code update. I'm
intending to wait until you let me know you want me to test
before trying again (on the PowerMac G5). (I've not been
testing on anything else: I did not intended to test
systems I've not seen a problem with until after the G5
seemed to be working.)
In part my waiting is because the first patch that I tried
left things unusable and I have to recover from the
consequences of a forced power off. It took a fair amount
of time.
I'd not be surprised if the G5 type of context has another
problem, separate from what I reported and what you are
working on. If so I may not be able to be an effective
tester: the fix may just repeat what I saw the first
time (based on a messed up context).
===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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