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Commit 10e6246e authored by Jens Axboe's avatar Jens Axboe
Browse files

block: document the 'io_poll_delay' queue sysfs file 



This was documented in the original commit, 64f1c21e, but it
never made it into the proper location for queue sysfs files.

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 542ff7bf

Documentation/block/queue-sysfs.txt

+14 −0
Original line number Diff line number Diff line
@@ -58,6 +58,20 @@ When read, this file shows the total number of block IO polls and how 
many returned success.  Writing '0' to this file will disable polling

for this device.  Writing any non-zero value will enable this feature.



io_poll_delay (RW)

------------------

If polling is enabled, this controls what kind of polling will be

performed. It defaults to -1, which is classic polling. In this mode,

the CPU will repeatedly ask for completions without giving up any time.

If set to 0, a hybrid polling mode is used, where the kernel will attempt

to make an educated guess at when the IO will complete. Based on this

guess, the kernel will put the process issuing IO to sleep for an amount

of time, before entering a classic poll loop. This mode might be a

little slower than pure classic polling, but it will be more efficient.

If set to a value larger than 0, the kernel will put the process issuing

IO to sleep for this amont of microseconds before entering classic

polling.



iostats (RW)

-------------

This file is used to control (on/off) the iostats accounting of the