Date: Fri, 5 Jun 2015 12:05:00 -0700 From: Neel Natu <neelnatu@gmail.com> To: Hans Petter Selasky <hps@selasky.org> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: [CFR] Replacing while loops with proper division and multiplication Message-ID: <CAFgRE9HQgM_NRDd2_qfVTaAwRURWO%2BRi-eJRp9-R1J2GY-DCWw@mail.gmail.com> In-Reply-To: <5571F02B.4080907@selasky.org> References: <55714B26.6060802@selasky.org> <CAFgRE9HOmzv%2BSuzWjsKDtsgRJCP3LpGJEQmd02_V=35__OE91A@mail.gmail.com> <5571F02B.4080907@selasky.org>
next in thread | previous in thread | raw e-mail | index | archive | help
Hi Hans,
On Fri, Jun 5, 2015 at 11:53 AM, Hans Petter Selasky <hps@selasky.org> wrote:
> On 06/05/15 20:31, Neel Natu wrote:
>>>>
>>>> - runs = 0;
>>>> >>- while (now >= state->nexthard) {
>>>> >>- state->nexthard += tick_sbt;
>>>> >>- runs++;
>>>> >>- }
>>>> >>- if (runs) {
>>>> >>+ runs = (now - state->nexthard) / tick_sbt;
>>>> >>+ if (runs > 0) {
>>>> >>+ printf("R%d ", (int)runs);
>>>> >>+ state->nexthard += tick_sbt * runs;
>>>> >> hct = DPCPU_PTR(hardclocktime);
>>>> >> *hct = state->nexthard - tick_sbt;
>>>> >> if (fake < 2) {
>>
>> There is a difference in behavior in the two implementations when 'now
>> == state->nexthard'. In the loop-based implementation this would end
>> up with 'runs = 1' whereas in the division-based implementation it
>> would end up with 'runs = 0'.
>>
>> I am not sure if this is intentional or just an oversight.
>
>
> Hi Neel,
>
> The nexthard is mainly updated in this piece of code. We can assume that
> "state->nexthard" is aligned to "ticks_sbt". If "state->nexthard % ticks_sbt
> == 0", is that still an issue?
>
I am not very familiar with this subsystem to make the call (mav@ or
davide@ would know for sure though).
I just noticed a discrepancy in the patch and wanted to highlight that
in case it might be an issue.
best
Neel
> --HPS
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAFgRE9HQgM_NRDd2_qfVTaAwRURWO%2BRi-eJRp9-R1J2GY-DCWw>