diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-block | 14 | ||||
| -rw-r--r-- | Documentation/block/biodoc.txt | 5 | ||||
| -rw-r--r-- | Documentation/percpu-rw-semaphore.txt | 27 |
3 files changed, 41 insertions, 5 deletions
diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block index c1eb41cb987..279da08f754 100644 --- a/Documentation/ABI/testing/sysfs-block +++ b/Documentation/ABI/testing/sysfs-block @@ -206,3 +206,17 @@ Description: when a discarded area is read the discard_zeroes_data parameter will be set to one. Otherwise it will be 0 and the result of reading a discarded area is undefined. + +What: /sys/block/<disk>/queue/write_same_max_bytes +Date: January 2012 +Contact: Martin K. Petersen <martin.petersen@oracle.com> +Description: + Some devices support a write same operation in which a + single data block can be written to a range of several + contiguous blocks on storage. This can be used to wipe + areas on disk or to initialize drives in a RAID + configuration. write_same_max_bytes indicates how many + bytes can be written in a single write same command. If + write_same_max_bytes is 0, write same is not supported + by the device. + diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index e418dc0a708..8df5e8e6dce 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt @@ -465,7 +465,6 @@ struct bio { bio_end_io_t *bi_end_io; /* bi_end_io (bio) */ atomic_t bi_cnt; /* pin count: free when it hits zero */ void *bi_private; - bio_destructor_t *bi_destructor; /* bi_destructor (bio) */ }; With this multipage bio design: @@ -647,10 +646,6 @@ for a non-clone bio. There are the 6 pools setup for different size biovecs, so bio_alloc(gfp_mask, nr_iovecs) will allocate a vec_list of the given size from these slabs. -The bi_destructor() routine takes into account the possibility of the bio -having originated from a different source (see later discussions on -n/w to block transfers and kvec_cb) - The bio_get() routine may be used to hold an extra reference on a bio prior to i/o submission, if the bio fields are likely to be accessed after the i/o is issued (since the bio may otherwise get freed in case i/o completion diff --git a/Documentation/percpu-rw-semaphore.txt b/Documentation/percpu-rw-semaphore.txt new file mode 100644 index 00000000000..7d3c8243190 --- /dev/null +++ b/Documentation/percpu-rw-semaphore.txt @@ -0,0 +1,27 @@ +Percpu rw semaphores +-------------------- + +Percpu rw semaphores is a new read-write semaphore design that is +optimized for locking for reading. + +The problem with traditional read-write semaphores is that when multiple +cores take the lock for reading, the cache line containing the semaphore +is bouncing between L1 caches of the cores, causing performance +degradation. + +Locking for reading is very fast, it uses RCU and it avoids any atomic +instruction in the lock and unlock path. On the other hand, locking for +writing is very expensive, it calls synchronize_rcu() that can take +hundreds of milliseconds. + +The lock is declared with "struct percpu_rw_semaphore" type. +The lock is initialized percpu_init_rwsem, it returns 0 on success and +-ENOMEM on allocation failure. +The lock must be freed with percpu_free_rwsem to avoid memory leak. + +The lock is locked for read with percpu_down_read, percpu_up_read and +for write with percpu_down_write, percpu_up_write. + +The idea of using RCU for optimized rw-lock was introduced by +Eric Dumazet <eric.dumazet@gmail.com>. +The code was written by Mikulas Patocka <mpatocka@redhat.com> |