On Wed, 6 Jun 2007 14:49:43 +0200, Oliver Neukum <[EMAIL PROTECTED]> wrote:
> Here's a patch to reduce padding: So, sizeofs are: original: 160 with anchor: 184 with the patch: 176 So, this does not win us back the space used for the anchor. We are still 16 bytes down, or about 10%. There's something you said in this thread which I would like to address. > > So, you add 24 bytes to all URBs, which are... not very thin, to be sure. > > Last time I counted they were 152 bytes apiece. Still, a 15% increase. > > I know you're a good algorithmist, are you sure you don't have any ideas? > > I figured the URB will end up in the same buckets for SLAB anyway due to > granularity. This is true, except for legacy cases (such as ub), where URBs are embedded into other objects. This relies on them not being ISO and thus being embeddable. But majority is allocated dynamically and all of them will be eventually. So, what do you think about moving the ISO descriptors out of line, and then allocating URBs out of a slab? Such a move would save tons on external fragmentation, enough for anchors and more. > Why do you care that much about the size of struct urb? There are a few > hundred of these structures at most at any given time. I think we gain more > in memory usage if we make using URBs easier, shrinking drivers' code. Firstly, we certainly are reasoning without data here. Your hunch that we'll win anything in driver code is not any better substantiated than my hunch that URBs are too big and cause memory pressure in unfortunate moments (otherwise, why does usb-storage continue to lock up with write throttling issues, but ub works in same tests). So, another reason why I like the slab is because it tells us how many are around. -- Pete ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
