Denis Vlasenko wrote:
Which shouldn't be true. There is no fundamental reason why
ordinary writes should be slower than O_DIRECT.
Again, there IS a reason: O_DIRECT eliminates the cpu overhead of the
kernel-user copy, and when coupled with multithreading or aio, allows
the IO queues to be kept full with useful transfers at all times.
Normal read/write requires the kernel to buffer and guess access
patterns correctly to perform read ahead and write behind perfectly to
keep the queues full. In practice, this does not happen perfectly all
of the time, or even most of the time, so it slows things down.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
