On 08/23/2017 11:39 AM, Dan Williams wrote:
> On Mon, Aug 21, 2017 at 2:11 PM, Dave Jiang <dave.jiang@xxxxxxxxx> wrote:
>> Adding a DMA supported blk-mq driver for pmem.
>
> "Add support for offloading pmem block-device I/O operations to a DMA engine."
>
>> This provides signficant CPU
>
> *significant
>
>> utilization reduction.
>
> "at the cost of some increased latency and bandwidth reduction in some cases."
>
>> By default the pmem driver will be using blk-mq with
>
> "By default the current cpu-copy based pmem driver will load, but this
> driver can be manually selected with a modprobe configuration."
>
>> DMA through the dmaengine API. DMA can be turned off with use_dma=0 kernel
>> parameter.
>
> Do we need the module option? It seems for debug / testing a user can
> simply unload the ioatdma driver, otherwise we should use dma by
> default.
>
>> Additional kernel parameters are provided:
>>
>> queue_depth: The queue depth for blk-mq. Typically in relation to what the
>> DMA engine can provide per queue/channel. This needs to take
>> into account of num_sg as well for some DMA engines. i.e.
>> num_sg * queue_depth < total descriptors available per queue or
>> channel.
>>
>> q_per_node: Hardware queues per node. Typically the number of channels the
>> DMA engine can provide per socket.
>> num_sg: Number of scatterlist we can handle per I/O request.
>
> Why do these need to be configurable?
The concern is with other arch/platforms that have different DMA
engines. The configurations would be platform dependent.
>
>>
>> Numbers below are measured against pmem simulated via DRAM using
>> memmap=NN!SS. DMA engine used is the ioatdma on Intel Skylake Xeon
>> platform. Keep in mind the performance for persistent memory
>> will differ.
>> Fio 2.21 was used.
>>
>> 64k: 1 task queuedepth=1
>> CPU Read: 7631 MB/s 99.7% CPU DMA Read: 2415 MB/s 54% CPU
>> CPU Write: 3552 MB/s 100% CPU DMA Write 2173 MB/s 54% CPU
>>
>> 64k: 16 tasks queuedepth=16
>> CPU Read: 36800 MB/s 1593% CPU DMA Read: 29100 MB/s 607% CPU
>> CPU Write 20900 MB/s 1589% CPU DMA Write: 23400 MB/s 585% CPU
>>
>> 2M: 1 task queuedepth=1
>> CPU Read: 6013 MB/s 99.3% CPU DMA Read: 7986 MB/s 59.3% CPU
>> CPU Write: 3579 MB/s 100% CPU DMA Write: 5211 MB/s 58.3% CPU
>>
>> 2M: 16 tasks queuedepth=16
>> CPU Read: 18100 MB/s 1588% CPU DMA Read: 21300 MB/s 180.9% CPU
>> CPU Write: 14100 MB/s 1594% CPU DMA Write: 20400 MB/s 446.9% CPU
>>
>> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
>> Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
>>
>> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
>> ---
>> drivers/nvdimm/Kconfig | 23 +
>> drivers/nvdimm/Makefile | 3
>> drivers/nvdimm/pmem.h | 3
>> drivers/nvdimm/pmem_mq.c | 853 ++++++++++++++++++++++++++++++++++++++++++++++
>> 4 files changed, 882 insertions(+)
>> create mode 100644 drivers/nvdimm/pmem_mq.c
>>
>> diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
>> index 5bdd499..c88c2bb 100644
>> --- a/drivers/nvdimm/Kconfig
>> +++ b/drivers/nvdimm/Kconfig
>> @@ -36,6 +36,29 @@ config BLK_DEV_PMEM
>>
>> Say Y if you want to use an NVDIMM
>>
>> +config BLK_DEV_PMEM_MQ
>
> Lets call the driver pmem_dma instead of pmem_mq, the "mq" is just a
> side effect of enabling dma support.
>
>> + tristate "PMEM: Persistent memory block device multi-queue support"
>> + depends on m
>
> Not sure what the exact kconfig syntax should be, but the policy I'm
> looking for is that this driver should be allowed to be built-in if
> the pmem driver is disabled.
>
>> + default LIBNVDIMM
>> + select DAX
>> + select ND_BTT if BTT
>> + select ND_PFN if NVDIMM_PFN
>
> I think these should probably move to a common symbol used by both
> pmem and pmem_dma.
>
>> + select DMA_ENGINE
>
> Shouldn't this be "depends on"?
>
>> + help
>> + Memory ranges for PMEM are described by either an NFIT
>> + (NVDIMM Firmware Interface Table, see CONFIG_NFIT_ACPI), a
>> + non-standard OEM-specific E820 memory type (type-12, see
>> + CONFIG_X86_PMEM_LEGACY), or it is manually specified by the
>> + 'memmap=nn[KMG]!ss[KMG]' kernel command line (see
>> + Documentation/admin-guide/kernel-parameters.rst). This driver
>> + converts these persistent memory ranges into block devices that are
>> + capable of DAX (direct-access) file system mappings. See
>> + Documentation/nvdimm/nvdimm.txt for more details. This driver
>> + utilizes block layer multi-queue in order to support using DMA
>> + engines to help offload the data copying.
>
> Rather than duplicating some of the pmem text I think this help text
> should only talk about the incremental differences relative to the
> base pmem driver.
>
>> +
>> + Say Y if you want to use an NVDIMM
>> +
>> config ND_BLK
>> tristate "BLK: Block data window (aperture) device support"
>> default LIBNVDIMM
>> diff --git a/drivers/nvdimm/Makefile b/drivers/nvdimm/Makefile
>> index 909554c..8bfd107 100644
>> --- a/drivers/nvdimm/Makefile
>> +++ b/drivers/nvdimm/Makefile
>> @@ -1,11 +1,14 @@
>> obj-$(CONFIG_LIBNVDIMM) += libnvdimm.o
>> obj-$(CONFIG_BLK_DEV_PMEM) += nd_pmem.o
>> +obj-$(CONFIG_BLK_DEV_PMEM_MQ) += nd_pmem_mq.o
>> obj-$(CONFIG_ND_BTT) += nd_btt.o
>> obj-$(CONFIG_ND_BLK) += nd_blk.o
>> obj-$(CONFIG_X86_PMEM_LEGACY) += nd_e820.o
>>
>> nd_pmem-y := pmem.o
>>
>> +nd_pmem_mq-y := pmem_mq.o
>> +
>
> s/mq/dma/
>
> I also think it's okay to drop the nd_ prefix for this.
>
>> nd_btt-y := btt.o
>>
>> nd_blk-y := blk.o
>> diff --git a/drivers/nvdimm/pmem.h b/drivers/nvdimm/pmem.h
>> index 5434321..bbbe982 100644
>> --- a/drivers/nvdimm/pmem.h
>> +++ b/drivers/nvdimm/pmem.h
>> @@ -4,6 +4,7 @@
>> #include <linux/types.h>
>> #include <linux/pfn_t.h>
>> #include <linux/fs.h>
>> +#include <linux/blk-mq.h>
>>
>> #ifdef CONFIG_ARCH_HAS_PMEM_API
>> #define ARCH_MEMREMAP_PMEM MEMREMAP_WB
>> @@ -35,6 +36,8 @@ struct pmem_device {
>> struct badblocks bb;
>> struct dax_device *dax_dev;
>> struct gendisk *disk;
>> + struct blk_mq_tag_set tag_set;
>> + struct request_queue *q;
>> };
>>
>> long __pmem_direct_access(struct pmem_device *pmem, pgoff_t pgoff,
>> diff --git a/drivers/nvdimm/pmem_mq.c b/drivers/nvdimm/pmem_mq.c
>> new file mode 100644
>> index 0000000..db2fc2a
>> --- /dev/null
>> +++ b/drivers/nvdimm/pmem_mq.c
>
> [snip bulk of driver code]
>
> Rather than copy-paste most of the existing pmem driver let's refactor
> all the common bits into a pmem-core module.
>
>> +MODULE_AUTHOR("Dave Jiang <dave.jiang@xxxxxxxxx>");
>
> Drop this MODULE_AUTHOR(), I think this is better handled with a
> MAINTAINERS entry.
>
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