On 3 December 2015 at 19:07, Zdenek Kabelac <zkabelac@xxxxxxxxxx> wrote: > Dne 3.12.2015 v 11:36 Baolin Wang napsal(a): > >> On 3 December 2015 at 10:56, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: >>> >>> On 3 December 2015 at 03:56, Alasdair G Kergon <agk@xxxxxxxxxx> wrote: >>>> >>>> On Wed, Dec 02, 2015 at 08:46:54PM +0800, Baolin Wang wrote: >>>>> >>>>> These are the benchmarks for request based dm-crypt. Please check it. >>>> >>>> >>>> Now please put request-based dm-crypt completely to one side and focus >>>> just on the existing bio-based code. Why is it slower and what can be >>>> adjusted to improve this? >>>> >>> >>> OK. I think I find something need to be point out. >>> 1. From the IO block size test in the performance report, for the >>> request based, we can find it can not get the corresponding >>> performance if we just expand the IO size. Because In dm crypt, it >>> will map the data buffer of one request with scatterlists, and send >>> all scatterlists of one request to the encryption engine to encrypt or >>> decrypt. I found if the scatterlist list number is small and each >>> scatterlist length is bigger, it will improve the encryption speed, >>> that helps the engine palys best performance. But a big IO size does >>> not mean bigger scatterlists (maybe many scatterlists with small >>> length), that's why we can not get the corresponding performance if we >>> just expand the IO size I think. >>> >>> 2. Why bio based is slower? >>> If you understand 1, you can obviously understand the crypto engine >>> likes bigger scatterlists to improve the performance. But for bio >>> based, it only send one scatterlist (the scatterlist's length is >>> always '1 << SECTOR_SHIFT' = 512) to the crypto engine at one time. It >>> means if the bio size is 1M, the bio based will send 2048 times (evey >>> time the only one scatterlist length is 512 bytes) to crypto engine to >>> handle, which is more time-consuming and ineffective for the crypto >>> engine. But for request based, it can map the whole request with many >>> scatterlists (not just one scatterlist), and send all the scatterlists >>> to the crypto engine which can improve the performance, is it right? >>> >>> Another optimization solution I think is we can expand the scatterlist >>> entry number for bio based. >>> >> >> I did some testing about my assumption of expanding the scatterlist >> entry number for bio based. I did some modification for the bio based >> to support multiple scatterlists, then it will get the same >> performance as the request based things. >> >> 1. bio based with expanding the scatterlist entry >> time dd if=/dev/dm-0 of=/dev/null bs=64K count=16384 iflag=direct >> 1073741824 bytes (1.1 GB) copied, 94.5458 s, 11.4 MB/s >> real 1m34.562s >> user 0m0.030s >> sys 0m3.850s >> >> 2. Sequential read 1G with requset based: >> time dd if=/dev/dm-0 of=/dev/null bs=64K count=16384 iflag=direct >> 1073741824 bytes (1.1 GB) copied, 94.8922 s, 11.3 MB/s >> real 1m34.908s >> user 0m0.030s >> sys 0m4.000s >> >> From the data, we can find the bio based also can get the same >> performance as the request based. So if someone still don't like the >> request based things, I think we can optimize the bio based by >> expanding the scatterlists number. Thanks. >> > > > Hi > > Do you see any performance impact if you use with cryptsetup options: > > --perf-same_cpu_crypt > --perf-submit_from_crypt_cpus > > with your regular unpatched kernel. I did not see the performance impact with these options you said, cause my board only has one cpu. > > Zdenek > -- Baolin.wang Best Regards -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
