[PATCH v2 0/2] qemu-qdisk: Implementation of grant copy operation.

[Paulina Szubarczyk <paulinaszubarczyk@gmail.com>]

Hi,

It is a proposition for implementation of grant copy operation in qemu-qdisk and 
interface in libxc/libs. 

Changes since v1:
Interface:
- changed the interface to call grant copy operation to match ioctl
	int xengnttab_grant_copy(xengnttab_handle *xgt,
                         	 uint32_t count,
                         	 xengnttab_grant_copy_segment_t* segs)

- added a struct 'xengnttab_copy_grant_segment' definition to tools/libs	
  /gnttab/private.h, tools/libxc/include/xenctrl_compat.h

- changed the function 'osdep_gnttab_grant_copy' which right now just
  call the ioctl

- added a new VER1.1 to tools/libs/gnttab/libxengnttab.map 

qemu-qdisk:
- removed the 'ioreq_write','ioreq_read_init','ioreq_read' functions 
- implemented 'ioreq_init_copy_buffers', 'ioreq_copy' 
- reverted the removal of grant map and introduced conditional invoking
  grant copy or grant map
- resigned from caching the local buffers on behalf of allocating the 
  required amount of pages at once. The cached structure would require 
  to have an lock guard and I suppose that the performance improvement 
  would degraded. 

For the functional test I attached the device with a qdisk backend to the guest, 
mounted, performed some reads and writes.

I run fio tests[1] with different iodepth and size of the block. The test can be 
accessed on my github[2] but mainly after the warm up I run for 60 seconds:
    fio --time_based \
		--clocksource=clock_gettime \
		--rw=randread \
		--random_distribution=pareto:0.9 \
		--size=10g \
	    --direct='1' \
	    --ioengine=libaio \
		--filename=$DEV \
		--iodepth=$IODEPTH \
		--bs=$BS \
		--name=$NAME \
		--runtime=$RUNTIME >> $FILENAME
The test were repeated at least three times. 

[1] https://docs.google.com/spreadsheets/d/1E6AMiB8ceJpExL6jWpH9u2yy6DZxzhmDUyFf-eUuJ0c/edit?usp=sharing

[2] https://github.com/paulina-szubarczyk/xen-benchmark
    - multitest_with_iodepth.sh


Thanks and regards, 
Paulina

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