Using O_DIRECT reduces the CPU load but the magical limit of 500 MB/s for one thread remains. Are the CRC sums calculated on a per thread base? Or stripe base? Is there a way to test the checksumming speed only?
Michael Am 20.10.2010 18:53, schrieb Andreas Dilger: > On 2010-10-20, at 10:40, Michael Kluge<[email protected]> wrote: >> It is the CPU load on the client. The dd/IOR process is using one core >> completely. The clients and the servers are connected via DDR IB. LNET >> bandwidth is at 1.8 GB/s. Servers have 1.8.3, the client has 1.8.3 patchless. > > If you only have a single threaded write, then this is somewhat unavoidable > to saturate a CPU due to copy_from_user(). O_DIRECT will avoid this. > > Also, disabling data checksums and debugging can help considerably. There > is a patch in bugzilla to add support for h/w crc32c on Nehalem CPUs to > reduce this overhead, but still not as fast as no checksum at all. > > Cheers, Andreas > >> Am 20.10.2010 18:15, schrieb Andreas Dilger: >>> Is this client CPU or server CPU? If you are using Ethernet it will >>> definitely be CPU hungry and can easily saturate a single core. >>> >>> Cheers, Andreas >>> >>> On 2010-10-20, at 8:41, Michael Kluge<[email protected]> wrote: >>> >>>> Hi list, >>>> >>>> is it normal, that a 'dd' or an 'IOR' pushing 10MB blocks to a lustre >>>> file system shows up with a 100% CPU load within 'top'? The reason why I >>>> am asking this is that I can write from one client to one OST with 500 >>>> MB/s. The CPU load will be at 100% in this case. If I stripe over two >>>> OSTs (which use different OSS servers and different RAID controllers) I >>>> will get 500 as well (seeing 2x250 MB/s on the OSTs). The CPU load will >>>> be at 100% again. >>>> >>>> A 'dd' on my desktop pushing 10M blocks to the local disk shows 7-10% >>>> CPU load. >>>> >>>> Are there ways to tune this behavior? Changing max_rpcs_in_flight and >>>> max_dirty_mb did not help. >>>> >>>> >>>> Regards, Michael >>>> >>>> -- >>>> >>>> Michael Kluge, M.Sc. >>>> >>>> Technische Universität Dresden >>>> Center for Information Services and >>>> High Performance Computing (ZIH) >>>> D-01062 Dresden >>>> Germany >>>> >>>> Contact: >>>> Willersbau, Room A 208 >>>> Phone: (+49) 351 463-34217 >>>> Fax: (+49) 351 463-37773 >>>> e-mail: [email protected] >>>> WWW: http://www.tu-dresden.de/zih >>>> _______________________________________________ >>>> Lustre-discuss mailing list >>>> [email protected] >>>> http://lists.lustre.org/mailman/listinfo/lustre-discuss >>> >> >> >> -- >> Michael Kluge, M.Sc. >> >> Technische Universität Dresden >> Center for Information Services and >> High Performance Computing (ZIH) >> D-01062 Dresden >> Germany >> >> Contact: >> Willersbau, Room WIL A 208 >> Phone: (+49) 351 463-34217 >> Fax: (+49) 351 463-37773 >> e-mail: [email protected] >> WWW: http://www.tu-dresden.de/zih > -- Michael Kluge, M.Sc. Technische Universität Dresden Center for Information Services and High Performance Computing (ZIH) D-01062 Dresden Germany Contact: Willersbau, Room WIL A 208 Phone: (+49) 351 463-34217 Fax: (+49) 351 463-37773 e-mail: [email protected] WWW: http://www.tu-dresden.de/zih _______________________________________________ Lustre-discuss mailing list [email protected] http://lists.lustre.org/mailman/listinfo/lustre-discuss
