lkml.org 
[lkml]   [2024]   [Jan]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] iio: gts-helper: Fix division loop
From
On 8/1/24 02:52, Jonathan Cameron wrote:
> On Thu, 4 Jan 2024 11:34:28 +0200
> Matti Vaittinen <mazziesaccount@gmail.com> wrote:
>
>> The loop based 64bit division may run for a long time when dividend is a
>> lot bigger than the divider. Replace the division loop by the
>> div64_u64() which implementation may be significantly faster.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
>> Fixes: 38416c28e168 ("iio: light: Add gain-time-scale helpers")
>
> Hmm. Fix or not perf improvement? I'm going to take the middle ground
> and leave the fixes tag, but not rush this in.
>
> So applied to the togreg branch of iio.git and for now just pushed out
> as testing for 0-day etc to take a look before I rebase that tree after
> rc1.
>
>
>
>> ---
>>
>> I've implemented also a fixup series for supporting rounding of
>> gains/scales:
>> https://lore.kernel.org/lkml/37d3aa193e69577353d314e94463a08d488ddd8d.1701780964.git.mazziesaccount@gmail.com/
>>
>> That series does also remove the offending loop.
>>
>> We don't currently have any in-tree users of GTS helpers which would
>> need the rounding support so pushing the rounding is not urgent (and I
>> haven't heard of Subjahit whose driver required the rounding). Hence, we
>> may want to only take this loop fix in for now (?) and reconsider
>> rounding when someone need that.
>>
>> Jonathan, what's your take on this?
> Agreed - let us wait for the rounding to have a user, but makes sense
> to tidy this corner up in the meantime.
>
> Thanks,
>
> Jonathan
>
>>
>> drivers/iio/industrialio-gts-helper.c | 5 ++---
>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iio/industrialio-gts-helper.c b/drivers/iio/industrialio-gts-helper.c
>> index 7653261d2dc2..abcab2d38589 100644
>> --- a/drivers/iio/industrialio-gts-helper.c
>> +++ b/drivers/iio/industrialio-gts-helper.c
>> @@ -34,7 +34,7 @@
>> static int iio_gts_get_gain(const u64 max, const u64 scale)
>> {
>> u64 full = max;
>> - int tmp = 1;
>> + int tmp = 0;
>>
>> if (scale > full || !scale)
>> return -EINVAL;
>> @@ -48,8 +48,7 @@ static int iio_gts_get_gain(const u64 max, const u64 scale)
>> tmp++;
>> }
>>
>> - while (full > scale * (u64)tmp)
>> - tmp++;
>> + tmp += div64_u64(full, scale);
>>
>> return tmp;
>> }
>>
>> base-commit: 2cc14f52aeb78ce3f29677c2de1f06c0e91471ab
>
>
Hi Matti,

Your fix works beautifully with the latest version of apds9306 driver which I am working on.
All available scale values can be set without any errors. Thank you.

Moving to a new city with a new full time job with the assumption of getting more time
for my list of opensource projects and contributions proved to be utterly wrong!

Regards,
Subhajit Ghosh

\
 
 \ /
  Last update: 2024-01-19 12:58    [from the cache]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and my Meterkast|Read the blog