[KPhotoAlbum] One final round of experiments...

[Robert Krawitz]

I tried a couple more things this evening, using lower quality JPEG
settings for reading images for building thumbnails and not opening
and closing the thumbnail file for each thumbnail written.

The first made very little difference; while loading JPEG files is
CPU-bound, decoding the JPEGs does not appear to constitute very much
of the load.

The second may have helped some loading files from an SSD if I
increased the number of scout threads.  2 scout threads currently
takes somewhere in the 3:50 range; with this change, it was closer to
3:40 with a reduction in system CPU time.  I was up around 480 MB/sec
whlie doing this, so fairly close to maxing out my SSD.  I'd really
need a faster processor, and even more importantly, an NVMe SSD, to
see whether this has much of an impact.  But the logic around it is a
bit complicated and it adds another lock, so there's some risk with
this change and hence I'm not pushing it to Load-performance.  I've
stuck it on another branch in case anyone wants to play with it (it's
called thumbnail-save-improvement).  If you have an NVMe SSD and a
very fast CPU with 6+ threads, I'd be interested in knowing whether
this makes a difference, but you will need to increase the scout
thread count to probably 3 to get the most benefit.  I have another
6-core system with a 3.3GHz base (i7-5820K), but its SSD is actually
slower than my laptop's.

Neither of these changes make a lick of difference on an HDD.  That's
not even close to CPU-bound on my system, and with one scout thread it
basically maxes out the disk.  Zero or two scout threads degrade
performance.

So as far as I'm concerned Load-performance is in its final state.
-- 
Robert Krawitz                                     <rlk at alum.mit.edu>

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