diff options
Diffstat (limited to 'Documentation/block/queue-sysfs.txt')
| -rw-r--r-- | Documentation/block/queue-sysfs.txt | 63 |
1 files changed, 57 insertions, 6 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt index e5d914845be6..2c1e67058fd3 100644 --- a/Documentation/block/queue-sysfs.txt +++ b/Documentation/block/queue-sysfs.txt @@ -14,6 +14,12 @@ add_random (RW) This file allows to turn off the disk entropy contribution. Default value of this file is '1'(on). +dax (RO) +-------- +This file indicates whether the device supports Direct Access (DAX), +used by CPU-addressable storage to bypass the pagecache. It shows '1' +if true, '0' if not. + discard_granularity (RO) ----------------------- This shows the size of internal allocation of the device in bytes, if @@ -37,15 +43,30 @@ large discards are issued, setting this value lower will make Linux issue smaller discards and potentially help reduce latencies induced by large discard operations. -discard_zeroes_data (RO) ------------------------- -When read, this file will show if the discarded block are zeroed by the -device or not. If its value is '1' the blocks are zeroed otherwise not. - hw_sector_size (RO) ------------------- This is the hardware sector size of the device, in bytes. +io_poll (RW) +------------ +When read, this file shows whether polling is enabled (1) or disabled +(0). 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 @@ -53,7 +74,7 @@ disk. logical_block_size (RO) ----------------------- -This is the logcal block size of the device, in bytes. +This is the logical block size of the device, in bytes. max_hw_sectors_kb (RO) ---------------------- @@ -141,6 +162,36 @@ control of this block device to that new IO scheduler. Note that writing an IO scheduler name to this file will attempt to load that IO scheduler module, if it isn't already present in the system. +write_cache (RW) +---------------- +When read, this file will display whether the device has write back +caching enabled or not. It will return "write back" for the former +case, and "write through" for the latter. Writing to this file can +change the kernels view of the device, but it doesn't alter the +device state. This means that it might not be safe to toggle the +setting from "write back" to "write through", since that will also +eliminate cache flushes issued by the kernel. + +write_same_max_bytes (RO) +------------------------- +This is the number of bytes the device can write in a single write-same +command. A value of '0' means write-same is not supported by this +device. +wb_lat_usec (RW) +---------------- +If the device is registered for writeback throttling, then this file shows +the target minimum read latency. If this latency is exceeded in a given +window of time (see wb_window_usec), then the writeback throttling will start +scaling back writes. Writing a value of '0' to this file disables the +feature. Writing a value of '-1' to this file resets the value to the +default setting. + +throttle_sample_time (RW) +------------------------- +This is the time window that blk-throttle samples data, in millisecond. +blk-throttle makes decision based on the samplings. Lower time means cgroups +have more smooth throughput, but higher CPU overhead. This exists only when +CONFIG_BLK_DEV_THROTTLING_LOW is enabled. Jens Axboe <jens.axboe@oracle.com>, February 2009 |