On Saturday 27 January 2007 15:01, Bodo Eggert wrote:Denis Vlasenko <vda.linux@xxxxxxxxxxxxxx> wrote:On Friday 26 January 2007 19:23, Bill Davidsen wrote:The kernel can also solve the halting problem if it can.Denis Vlasenko wrote:It is not required by any standard that I know. Kernel can be smarterOn Thursday 25 January 2007 21:45, Michael Tokarev wrote:Other than the copy to buffer taking CPU and memory resources.But even single-threaded I/O but in large quantities benefits fromWhich shouldn't be true. There is no fundamental reason why
O_DIRECT significantly, and I pointed this out before.
ordinary writes should be slower than O_DIRECT.
and avoid that if it can.
Do you really think an entropy estamination code on all access patterns in the
system will be free as in beer,
Actually I think we need this heuristic:
if (opened_with_O_STREAM && buffer_is_aligned
&& io_size_is_a_multiple_of_sectorsize)
do_IO_directly_to_user_buffer_without_memcpy
is not *that* compilcated.
I think that we can get rid of O_DIRECT peculiar requirements
"you *must* not cache me" + "you *must* write me directly to bare metal"
by replacing it with O_STREAM ("*advice* to not cache me") + O_SYNC
("write() should return only when data is written to storage, not sooner").
Why?
Because these O_DIRECT "musts" are rather unusual and overkill. Apps
should not have that much control over what kernel does internally;
and also O_DIRECT was mixing shampoo and conditioner on one bottle
(no-cache and sync writes) - bad API.