hdparm can be used to get disk reading performance with following command line:
- hdparm -T <dev>. Get cached disk reading performance. In fact, the page cache performance is tested.
- hdparm -t <dev>. Get raw disk reading performance.
Implementation
hdparm -T
ioctl(devfd, BLKFLSBUF, NULL);
read(devfd, buf, READING_SIZE)
do {
seek(devfd, 0, SEEK_SET);
read(devfd, buf, READING_SIZE);
} while (/* time is not over */);
Because the data to be read is in page cache always (if READING_SIZE << memory size), the result is page cache performance.
hdparm -t
ioctl(devfd, BLKFLSBUF, NULL);
do {
read(devfd, buf, READING_SIZE);
} while (/* time is not over */);
Because the data to be read is not in page cache, and the bottleneck lies in raw disk reading speed, the result is raw disk reading performance.
reading prepare * * *
memory copy - -
raw disk read ++++++++ ++++++++
As in above figure, reading reparation and memory copying in testing is neglectable, especially when readahead is considered.
