A few performance tests on sequential file read methods under Windows

After reading Timothy Farrar's post on I/O thread scheduling, I thought that I made my latest performance tests on File I/O (especially read) too long ago.

I took some time to build a few no-brainer test functions, reading a file of about 1Gb, all read requests are 64Kb.

I essentially tested different a few variations :

• STDIO - standard stdio streams
• STD_S - standard stdio streams + 'sequential' microsoft extension (fopen(filename, "rbS"))
• WIN32 - Win32 API CreateFile using FILE_ATTRIBUTE_NORMAL
• WINNB - Win32 API CreateFile using FILE_FLAG_NO_BUFFERING
• MAPPB - Mapped file input (unrealistically mapping the whole file, and lazily using boost::iostreams::mapped_file)

As I'm not currently interested in latency, but more in brute-force throughput, I did not bother tested any async I/O.

On the same file, on the same hard drive (Seagate ST3250410AS), on the same machine, I ran the test on an XP32 and a Vista64.

To make it short, timings follow, it seems that :

• under XP32, using FILE_FLAG_NO_BUFFERING is worth the hassle. For lazy people, using Microsoft extension to fopen ("rbS" mode) looks like an easy good win.
• under Vista64, memory mapped file is the slowest approach, and all others compare almost equal, with a win for fopen in "rbS" mode.

I made quick tests on other machines, and the trends are the same.

XP32

Y:\>bench_disk_access_code.exe f:\ortho1.megatex
STDIO f:\ortho1.megatex : 33.35 Mb/sec. - 995754.00 Kb
WIN32 f:\ortho1.megatex : 33.57 Mb/sec. - 995754.00 Kb
STD_S f:\ortho1.megatex : 68.37 Mb/sec. - 995754.00 Kb
WINNB f:\ortho1.megatex : 87.09 Mb/sec. - 995754.00 Kb
MAPPD f:\ortho1.megatex : 79.23 Mb/sec. - 995754.00 Kb

Vista64

Y:\>bench_disk_access_code.exe f:\ortho1.megatex
STDIO f:\ortho1.megatex : 86.45 Mb/sec. - 995754.00 Kb
WIN32 f:\ortho1.megatex : 86.94 Mb/sec. - 995754.00 Kb
STD_S f:\ortho1.megatex : 88.42 Mb/sec. - 995754.00 Kb
WINNB f:\ortho1.megatex : 86.82 Mb/sec. - 995754.00 Kb
MAPPD f:\ortho1.megatex : 76.58 Mb/sec. - 995754.00 Kb