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Re: My take on the diff-optimizations-bytes branch

From: Stefan Fuhrmann <eqfox_at_web.de>
Date: Wed, 26 Jan 2011 22:13:39 +0100

On 26.01.2011 03:09, Johan Corveleyn wrote:
> On Tue, Jan 25, 2011 at 1:37 AM, Stefan Fuhrmann<eqfox_at_web.de> wrote:
> [ ... snip ...]
>> And, as promised, here some ideas how to get more
>> speed from the generic code. Your latest commit:
>>
>> +#if SVN_UNALIGNED_ACCESS_IS_OK
>> +
>> + /* Skip quickly over the stuff between EOLs. */
>> + for (i = 0, can_read_word = TRUE; i< file_len; i++)
>> + can_read_word = can_read_word
>> +&& (file[i].curp + sizeof(apr_size_t)< file[i].endp);
>> + while (can_read_word)
>> + {
>> + for (i = 1, is_match = TRUE; i< file_len; i++)
>> + is_match = is_match
>> +&& ( *(const apr_size_t *)file[0].curp
>> + == *(const apr_size_t *)file[i].curp);
>> +
>> + if (!is_match || contains_eol(*(const apr_size_t *)file[0].curp))
>> + break;
>> +
>> + for (i = 0; i< file_len; i++)
>> + file[i].curp += sizeof(apr_size_t);
>> + for (i = 0, can_read_word = TRUE; i< file_len; i++)
>> + can_read_word = can_read_word
>> +&& (file[i].curp + sizeof(apr_size_t)< file[i].endp);
>> + }
>> +
>> +#endif
>>
>> could be changed to something like the following.
>> Please note that I haven't tested any of this:
> Thanks. There was one error in your suggestion, which I found out
> after testing. See below.
I was afraid so. I just hacked the code directly
into Thunderbird and was unsure whether the
exit behavior was correct.
>> /* Determine how far we may advance with chunky ops without reaching
>> * endp for any of the files.
>> * Signedness is important here if curp gets close to endp.
>> */
>> apr_ssize_t max_delta = file[0].endp - file[0].curp - sizeof(apr_size_t);
>> for (i = 1; i< file_len; i++)
>> {
>> apr_ssize_t delta = file[i].endp - file[i].curp - sizeof(apr_size_t);
>> if (delta< max_delta)
>> max_delta = delta;
>> }
>>
>> /* the former while() loop */
>> is_match = TRUE;
>> for (delta = 0; delta< max_delta&& is_match; delta += sizeof(apr_size_t))
>> {
>> apr_size_t chunk = *(const apr_size_t *)(file[0].curp + delta);
>> if (contains_eol(chunk))
>> break;
>>
>> for (i = 1; i< file_len; i++)
>> if (chunk != *(const apr_size_t *)(file[i].curp + delta))
>> {
>> is_match = FALSE;
> Here, I inserted:
>
> delta -= sizeof(apr_size_t);
>
> because otherwise, delta will be increased too far (it will still be
> increased by the counting expression of the outer for-loop (after
> which it will stop because of !is_match)). Maybe there is a
> cleaner/clearer way to break out of the outer for-loop here, without
> incrementing delta again, but for now, I've committed it with this
> change (r1063565).
Yeah, I really wished for a "goto" there. The clean
solution, I guess, would be moving that section to
some sub-routine returning the final value of delta.
>> break;
>> }
>> }
>>
>> /* We either found a mismatch or an EOL at or shortly behind curp+delta
>> * or we cannot proceed with chunky ops without exceeding endp.
>> * In any way, everything up to curp + delta is equal and not an EOL.
>> */
>> for (i = 0; i< file_len; i++)
>> file[i].curp += delta;
> Thanks. This gives on my machine/example another 15-20% performance
> increase (datasources_open time going down from ~21 s to ~17 s). We
> should probably do the same for suffix scanning, but I'm too tired
> right now :-) (and suffix scanning is more difficult to grok, so not a
> good idea to do at 3 am).
Don't get yourself burned out ;)

-- Stefan^2.
Received on 2011-01-26 22:15:57 CET

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