From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: Deepak R Varma <mh12gx2825@gmail.com>,
outreachy-kernel@googlegroups.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Daniel Baluta <daniel.baluta@gmail.com>,
kieran.bingham@ideasonboard.com,
Lars-Peter Clausen <lars@metafoo.de>,
Michael Hennerich <Michael.Hennerich@analog.com>,
Jonathan Cameron <jic23@kernel.org>,
Hartmut Knaack <knaack.h@gmx.de>,
Peter Meerwald <pmeerw@pmeerw.net>,
linux-iio <linux-iio@vger.kernel.org>
Subject: Re: [Outreachy kernel] Re: [PATCH v3 3/4] staging: iio: adc: ad7192: get_filter_freq code optimization
Date: Mon, 23 Mar 2020 11:28:52 +0200 [thread overview]
Message-ID: <CAHp75VfF+oDWsOF+_=U6YBeP60XLF=SLYzExa=5WjLSgoMUw9A@mail.gmail.com> (raw)
In-Reply-To: <20200323014935.48048405@elisabeth>
On Mon, Mar 23, 2020 at 2:49 AM Stefano Brivio <sbrivio@redhat.com> wrote:
> On Mon, 23 Mar 2020 01:44:20 +0200
> Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> > On Sun, Mar 22, 2020 at 9:57 PM Deepak R Varma <mh12gx2825@gmail.com> wrote:
> > >
> > > Current implementation of the function ad7192_get_available_filter_freq
> > > repeats calculation of output data rate a few times. We can simplify
> > > these steps by refactoring out the calculation of fADC. This would also
> > > addresses the checkpatch warning of line exceeding 80 character.
> >
> > I'm not sure you did an equivalent changes. I believe in the original
> > code precision is better. Consider low clock frequencies when 10 bit
> > right shift may hide some bits of the division.
>
> Note that those bits are eventually "hidden" in the same way later,
Even if mathematically (arithmetically) evaluation is correct, we have
to remember that computers are bad with floating point and especially
kernel, which uses integer arithmetic. That said, it's easy to get
off-by-one error (due to precision lost) if we do big division before
(not so big) multiplication.
> despite the different sequence, due to DIV_ROUND_CLOSEST() being used
> at every step (both before and after the change) without other
> operations occurring.
By the way, where AD7192_SINC3_FILTER and AD7192_SINC4_FILTER
multiplications disappear and why?
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-03-23 9:29 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-22 19:53 [PATCH v3 0/4] staging: iio: adc: General code reformatting / cleanup patchset Deepak R Varma
2020-03-22 19:54 ` [PATCH v3 1/4] staging: iio: adc: ad7192: Re-indent enum labels Deepak R Varma
2020-03-24 7:18 ` Ardelean, Alexandru
2020-03-26 8:19 ` Ardelean, Alexandru
2020-03-26 8:22 ` Ardelean, Alexandru
2020-03-22 19:55 ` [PATCH v3 2/4] staging: iio: adc: ad7192: Correct macro names from SYNC to SINC Deepak R Varma
2020-03-22 23:40 ` Andy Shevchenko
2020-03-23 17:50 ` DEEPAK VARMA
2020-03-26 8:20 ` Ardelean, Alexandru
2020-03-22 19:56 ` [PATCH v3 3/4] staging: iio: adc: ad7192: get_filter_freq code optimization Deepak R Varma
2020-03-22 23:44 ` Andy Shevchenko
2020-03-23 0:49 ` [Outreachy kernel] " Stefano Brivio
2020-03-23 9:28 ` Andy Shevchenko [this message]
2020-03-23 12:15 ` Stefano Brivio
2020-03-23 17:52 ` DEEPAK VARMA
2020-03-24 8:06 ` Ardelean, Alexandru
2020-03-25 17:38 ` DEEPAK VARMA
2020-03-25 19:37 ` Andy Shevchenko
2020-03-25 19:59 ` Stefano Brivio
2020-03-26 8:15 ` Ardelean, Alexandru
2020-03-22 19:57 ` [PATCH v3 4/4] staging: iio: adc: ad7280a: Add comments to clarify stringified arguments Deepak R Varma
2020-03-24 8:07 ` Ardelean, Alexandru
2020-03-28 13:28 ` Jonathan Cameron
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