2011/8/5 Kevin Wolf <kw...@redhat.com>: > Am 03.08.2011 15:39, schrieb Frediano Ziglio: >> 2011/8/2 Kevin Wolf <kw...@redhat.com>: >>> Am 02.08.2011 17:29, schrieb Frediano Ziglio: >>>>>> - L2 allocation can be done with relative data (this is not easy to do >>>>>> with current code) >>>>> >>>>> What do you mean by that? >>>>> >>>> >>>> Let's take an example. By allocation I mean give a position to >>>> data/l2/refcount_table. Usually you cannot update/write L2 before data >>>> is allocated and written if you don't want to get a L2 entry pointing >>>> to garbage or unwritten data (if physically you write to a sector you >>>> get new data or old one on fail, not data changing to anything else). >>>> The exception to this is when even L2 table is not allocated. In this >>>> case you can write L2 table with data cause in case of failure this >>>> new L2 table is just not attached to anything (cause L1 still point to >>>> old L2 or is not allocated). My patch can collapse these two cluster >>>> writes in a single one. The key point of the patch is mainly >>>> collapsing all writes as you can not blocking other writes if not >>>> needed. >>> >>> Ok, I see. >>> >>> Not sure if it makes any measurable difference. With 64k clusters, an L2 >>> allocation happens only every 512 MB. But if it's not much code to >>> support it, it's probably a good thing. >>> >> >> Let's see :) >> >> I published a repo at gitorious. https://gitorious.org/qemu (yes, qemu >> was free for me :) ) > > Pretty radical changes. :-) > > I didn't really read most of the code (yet), but I gave it a try and ran > an iozone benchmark with it. It seems to degrade cluster allocation > performance to about the level of qcow2 in 0.12.4. > > The numbers say that you get about 40% of git master throughput on large > block sizes (256k), and 65% of git master throughput on small ones (8k). > So you may really have triggered some special cases that only apply for > qemu-io/qemu-img. > > Kevin >
I'll try iozone too. I have still to try real tests. It seems that many performance boost I can get with qcow2x can be implemented without changing so much code in qcow2. Perhaps I posted my code too much earlier. Which iozone tests are you running? Frediano
