From: David Howells <dhowells@redhat•com>
To: Andy Shevchenko <andriy.shevchenko@linux•intel.com>
Cc: Sam Bobroff <sbobroff@linux•ibm.com>,
linux-pci@vger•kernel.org, dhowells@redhat•com,
Oliver O'Halloran <oohall@gmail•com>,
Bjorn Helgaas <helgaas@kernel•org>,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH v1 1/2] PCI/AER: Use for_each_set_bit()
Date: Wed, 02 Oct 2019 11:27:59 +0100 [thread overview]
Message-ID: <11309.1570012079@warthog.procyon.org.uk> (raw)
In-Reply-To: <20190930121313.GV32742@smile.fi.intel.com>
Andy Shevchenko <andriy.shevchenko@linux•intel.com> wrote:
> > but I confess to being a little ambivalent. It's
> > arguably a little easier to read,
>
> I have another opinion here. Instead of parsing body of for-loop, the name of
> the function tells you exactly what it's done. Besides the fact that reading
> and parsing two lines, with zero conditionals, is faster.
>
> > but it's not nearly as efficient
> > (not a great concern here)
>
> David, do you know why for_each_set_bit() has no optimization for the cases
> when nbits <= BITS_PER_LONG? (Actually find_*bit() family of functions)
I've not had anything to do with for_each_set_bit() itself.
By 'nbits', I presume you mean the size parameter - max in the sample bit of
code.
It would need per-arch optimisation. Some arches have an instruction to find
the next bit and some don't.
Using for_each_set_bit() like this is definitely suboptimal, since
find_first_bit() and find_next_bit() may well be out of line.
It should probably be using something like __ffs() if size <= BITS_PER_LONG.
David
prev parent reply other threads:[~2019-10-02 10:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-27 15:18 [PATCH v1 1/2] PCI/AER: Use for_each_set_bit() Andy Shevchenko
2019-08-27 15:18 ` [PATCH v1 2/2] PCI/AER: Update parameter descriptions to satisfy kernel-doc validator Andy Shevchenko
2019-08-27 17:06 ` Kuppuswamy Sathyanarayanan
2019-08-28 10:07 ` Andy Shevchenko
2019-08-27 17:06 ` [PATCH v1 1/2] PCI/AER: Use for_each_set_bit() Kuppuswamy Sathyanarayanan
2019-09-27 10:44 ` Bjorn Helgaas
2019-09-27 12:39 ` Bjorn Helgaas
2019-09-30 12:13 ` Andy Shevchenko
2019-10-02 10:27 ` David Howells [this message]
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