Re: [PATCH 1/1] pmem: allow user to set QUEUE_FLAG_NOWAIT

[Ira Weiny <ira.weiny@intel.com>]

Chaitanya Kulkarni wrote:
> Allow user to set the QUEUE_FLAG_NOWAIT optionally using module
> parameter to retain the default behaviour. Also, update respective
> allocation flags in the write path. Following are the performance
> numbers with io_uring fio engine for random read, note that device has
> been populated fully with randwrite workload before taking these
> numbers :-

I'm not seeing any comparison with/without the option you propose?  I
assume there is some performance improvement you are trying to show?

> 
> * linux-block (for-next) # grep IOPS  pmem*fio | column -t
> 
> nowait-off-1.fio:  read:  IOPS=3968k,  BW=15.1GiB/s
> nowait-off-2.fio:  read:  IOPS=4084k,  BW=15.6GiB/s
> nowait-off-3.fio:  read:  IOPS=3995k,  BW=15.2GiB/s
> 
> nowait-on-1.fio:   read:  IOPS=5909k,  BW=22.5GiB/s
> nowait-on-2.fio:   read:  IOPS=5997k,  BW=22.9GiB/s
> nowait-on-3.fio:   read:  IOPS=6006k,  BW=22.9GiB/s
> 
> * linux-block (for-next) # grep cpu  pmem*fio | column -t
> 
> nowait-off-1.fio:  cpu  :  usr=6.38%,   sys=31.37%,  ctx=220427659
> nowait-off-2.fio:  cpu  :  usr=6.19%,   sys=31.45%,  ctx=229825635
> nowait-off-3.fio:  cpu  :  usr=6.17%,   sys=31.22%,  ctx=221896158
> 
> nowait-on-1.fio:  cpu  :  usr=10.56%,  sys=87.82%,  ctx=24730   
> nowait-on-2.fio:  cpu  :  usr=9.92%,   sys=88.36%,  ctx=23427   
> nowait-on-3.fio:  cpu  :  usr=9.85%,   sys=89.04%,  ctx=23237   
> 
> * linux-block (for-next) # grep slat  pmem*fio | column -t
> nowait-off-1.fio:  slat  (nsec):  min=431,   max=50423k,  avg=9424.06
> nowait-off-2.fio:  slat  (nsec):  min=420,   max=35992k,  avg=9193.94
> nowait-off-3.fio:  slat  (nsec):  min=430,   max=40737k,  avg=9244.24
> 
> nowait-on-1.fio:   slat  (nsec):  min=1232,  max=40098k,  avg=7518.60
> nowait-on-2.fio:   slat  (nsec):  min=1303,  max=52107k,  avg=7423.37
> nowait-on-3.fio:   slat  (nsec):  min=1123,  max=40193k,  avg=7409.08
> 
> Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
> ---
>  drivers/nvdimm/pmem.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index ceea55f621cc..38defe84de4c 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -31,6 +31,10 @@
>  #include "pfn.h"
>  #include "nd.h"
>  
> +static bool g_nowait;
> +module_param_named(nowait, g_nowait, bool, 0444);
> +MODULE_PARM_DESC(nowait, "set QUEUE_FLAG_NOWAIT. Default: False");

Module parameters should be avoided.  Since I'm not clear on the
performance benefit I can't comment on alternatives.  But I strongly
suspect that this choice is not going to be desired for all devices
always.

Ira

> +
>  static struct device *to_dev(struct pmem_device *pmem)
>  {
>  	/*
> @@ -543,6 +547,8 @@ static int pmem_attach_disk(struct device *dev,
>  	blk_queue_max_hw_sectors(q, UINT_MAX);
>  	blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
>  	blk_queue_flag_set(QUEUE_FLAG_SYNCHRONOUS, q);
> +	if (g_nowait)
> +		blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
>  	if (pmem->pfn_flags & PFN_MAP)
>  		blk_queue_flag_set(QUEUE_FLAG_DAX, q);
>  
> -- 
> 2.40.0
>