On Sat, May 16, 2015 at 6:19 PM, Elliott, Robert (Server Storage) <elli...@hp.com> wrote: > >> -----Original Message----- >> From: Linux-nvdimm [mailto:linux-nvdimm-boun...@lists.01.org] On Behalf Of >> Dan Williams >> Sent: Tuesday, April 28, 2015 1:26 PM >> To: linux-nvd...@lists.01.org >> Cc: Ingo Molnar; Neil Brown; Greg KH; Dave Chinner; linux- >> ker...@vger.kernel.org; Andy Lutomirski; Jens Axboe; H. Peter Anvin; >> Christoph Hellwig >> Subject: [Linux-nvdimm] [PATCH v2 19/20] nd_btt: atomic sector updates >> >> From: Vishal Verma <vishal.l.ve...@linux.intel.com> >> >> BTT stands for Block Translation Table, and is a way to provide power >> fail sector atomicity semantics for block devices that have the ability >> to perform byte granularity IO. It relies on the ->rw_bytes() capability >> of provided nd namespace devices. >> >> The BTT works as a stacked blocked device, and reserves a chunk of space >> from the backing device for its accounting metadata. BLK namespaces may >> mandate use of a BTT and expect the bus to initialize a BTT if not >> already present. Otherwise if a BTT is desired for other namespaces (or >> partitions of a namespace) a BTT may be manually configured. > ... > > Running btt above pmem with a variety of workloads, I see an awful lot > of time spent in two places: > * _raw_spin_lock > * btt_make_request > > This occurs for fio to raw /dev/ndN devices, ddpt over ext4 or xfs, > cp -R of large directories, and running make on the linux kernel. > > Some specific results: > > fio 4 KiB random reads, WC cache type, memcpy: > * 43175 MB/s, 8 M IOPS pmem0 and pmem1 > * 18500 MB/s, 1.5 M IOPS nd0 and nd1 > > fio 4 KiB random reads, WC cache type, memcpy with non-temporal > loads (when everything is 64-byte aligned): > * 33814 MB/s, 4.3 M IOPS nd0 and nd1 > > Zeroing out 32 MiB with ddpt: > * 19 s, 1800 MiB/s pmem > * 55 s, 625 MiB/s btt > > If btt_make_request needs to stall this much, maybe it'd be better > to utilize the blk-mq request queues, keeping requests in per-CPU > queues while they're waiting, and using IPIs for completion > interrupts when they're finally done.
2 items to check: 1/ make sure you have a your btt sector size set to 4k which cuts down the overhead by a factor of 8. 2/ boot with nr_cpus=256 or lower. Ross noticed that CONFIG_NR_CPUS is set quite high on distro kernels which revealed that we should have been using nr_cpu_ids and percpu variables for nd_region_acquire_lane() from the outset. This fix is coming in v3. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
