在 2024/7/30 18:42, Christian König 写道:
Am 30.07.24 um 11:05 schrieb Huan Yang:
在 2024/7/30 16:56, Daniel Vetter 写道:
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On Tue, Jul 30, 2024 at 03:57:44PM +0800, Huan Yang wrote:
UDMA-BUF step:
1. memfd_create
2. open file(buffer/direct)
3. udmabuf create
4. mmap memfd
5. read file into memfd vaddr
Yeah this is really slow and the worst way to do it. You absolutely
want
to start _all_ the io before you start creating the dma-buf, ideally
with
everything running in parallel. But just starting the direct I/O with
async and then creating the umdabuf should be a lot faster and avoid
That's greate, Let me rephrase that, and please correct me if I'm
wrong.
UDMA-BUF step:
1. memfd_create
2. mmap memfd
3. open file(buffer/direct)
4. start thread to async read
3. udmabuf create
With this, can improve
needlessly serialization operations.
The other issue is that the mmap has some overhead, but might not be
too
bad.
Yes, the time spent on page fault in mmap should be negligible
compared to the time spent on file read.
You should try to avoid mmap as much as possible. Especially the TLB
invalidation overhead is really huge on platforms with a large number
of CPUs.
But, if not mmap, how to read file from fd to fd? sendfile may
help(shmemfs may support it, I do not test it), but use pipe buffer is
not good through test.
Regards,
Christian.
-Sima
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch/
