linux-kernel - Re: [PATCH] dax: Fix missed PMD wakeups

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Date:   Thu, 4 Jul 2019 17:32:23 +0300
From:   Boaz Harrosh <openosd@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>, stable <stable@...r.kernel.org>,
        Robert Barror <robert.barror@...el.com>,
        Seema Pandit <seema.pandit@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dax: Fix missed PMD wakeups

On 04/07/2019 16:58, Matthew Wilcox wrote:
> On Thu, Jul 04, 2019 at 04:00:00PM +0300, Boaz Harrosh wrote:
<>
>> Matthew you must be kidding an ilog2 in binary is zero clocks
>> (Return the highest bit or something like that)
> 
> You might want to actually check the documentation instead of just
> making shit up.
> 

Yes you are right I stand corrected. Must be smoking ;-)

> https://www.agner.org/optimize/instruction_tables.pdf
> 
> I think in this instance what we want is BSR (aka ffz) since the input is
> going to be one of 0, 1, 3, 7, 15 or 31 (and we want 0, 1, 2, 3, 4, 5 as
> results).
> 
<>
> The compiler doesn't know the range of 'sibs'.  Unless we do the
> profile-feedback thing.
> 

Would you please consider the use of get_order() macro from #include <getorder.h>
Just for the sake of understanding? (Or at least a comment)

Thanks
Boaz