Preliminary results of using multiblock raw I/O

Shailabh Nagar (nagar@us.ibm.com)
Fri, 19 Oct 2001 14:03:46 -0400


Following up on the previous mail with patches for doing multiblock raw I/O
:

Experiments on a 2-way, 850MHz PIII, 256K cache, 256M memory
Running bonnie (modified to allow specification of O_DIRECT option,
target file etc.)
Only the block tests (rewrite,read,write) have been run. All tests
are single threaded.

BW = bandwidth in kB/s
cpu = %CPU use
abs = size of each I/O request
(NOT blocksize used by underlying raw I/O mechanism !)

pre2 = using kernel 2.4.13-pre2aa1
multi = 2.4.13-pre2aa1 kernel with multiblock raw I/O patches applied
(both /dev/raw and O_DIRECT)

/dev/raw (uses 512 byte blocks)
===============================

rewrite write read
------------------------------------------------------------------
pre2 multi pre2 multi pre2 multi
------------------------------------------------------------------
abs BW cpu BW cpu BW cpu BW cpu BW cpu BW cpu
------------------------------------------------------------------
4k 884 0.5 882 0.1 1609 0.3 1609 0.2 9841 1.5 9841 0.9
6k 884 0.5 882 0.2 1609 0.5 1609 0.1 9841 1.8 9841 1.2
16k 884 0.6 882 0.2 1609 0.3 1609 0.0 9841 2.7 9841 1.4
18k 884 0.4 882 0.2 1609 0.4 1607 0.1 9841 2.4 9829 1.2
64k 883 0.5 882 0.1 1609 0.4 1609 0.3 9841 2.0 9841 0.6
66k 883 0.5 882 0.2 1609 0.5 1609 0.2 9829 3.4 9829 1.0

O_DIRECT : on filesystem with 1K blocksize
===========================================

rewrite write read
------------------------------------------------------------------
pre2 multi pre2 multi pre2 multi
------------------------------------------------------------------
abs BW cpu BW cpu BW cpu BW cpu BW cpu BW cpu
------------------------------------------------------------------
4k 854 0.8 880 0.4 1527 0.5 1607 0.1 9731 2.5 9780 1.3
6k 856 0.4 882 0.3 1527 0.4 1607 0.1 9732 1.6 9780 0.7
16k 857 0.4 881 0.1 1527 0.3 1608 0.0 9732 2.2 9780 1.2
18k 857 0.3 882 0.2 1527 0.4 1607 0.1 9731 1.9 9780 1.0
64k 857 0.3 881 0.1 1526 0.4 1607 0.2 9732 1.6 9780 1.6
66k 856 0.4 882 0.2 1527 0.4 1607 0.2 9731 2.7 9780 1.2

Shailabh Nagar
Enterprise Linux Group, IBM TJ Watson Research Center
(914) 945 2851, T/L 862 2851

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