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Date: Thu, 14 Aug 2008 18:17:15 +1000 From: Aaron Carroll <aaronc@...ato.unsw.edu.au> To: jens.axboe@...cle.com Cc: linux-kernel@...r.kernel.org Subject: [PATCH 3/3] block: update documentation for deadline fifo_batch tunable Update the description of fifo_batch to match the current implementation, and include a description of how to tune it. Signed-off-by: Aaron Carroll <aaronc@...ato.unsw.edu.au> --- Documentation/block/deadline-iosched.txt | 14 ++++++++++---- 1 files changed, 10 insertions(+), 4 deletions(-) diff --git a/Documentation/block/deadline-iosched.txt b/Documentation/block/deadline-iosched.txt index c23cab1..7257676 100644 --- a/Documentation/block/deadline-iosched.txt +++ b/Documentation/block/deadline-iosched.txt @@ -30,12 +30,18 @@ write_expire (in ms) Similar to read_expire mentioned above, but for writes. -fifo_batch +fifo_batch (number of requests) ---------- -When a read request expires its deadline, we must move some requests from -the sorted io scheduler list to the block device dispatch queue. fifo_batch -controls how many requests we move. +Requests are grouped into ``batches'' of a particular data direction (read or +write) which are serviced in increasing sector order. To limit extra seeking, +deadline expiries are only checked between batches. fifo_batch controls the +maximum number of requests per batch. + +This parameter tunes the balance between per-request latency and aggregate +throughput. When low latency is the primary concern, smaller is better (where +a value of 1 yields first-come first-served behaviour). Increasing fifo_batch +generally improves throughput, at the cost of latency variation. writes_starved (number of dispatches) -- 1.5.4.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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