Messages in this thread | | | From | Blaisorblade <> | Subject | Re: [patch 1/1] uml: fixes performance regression in activate_mm and thus exec() | Date | Tue, 23 Aug 2005 11:57:15 +0200 |
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On Friday 12 August 2005 22:11, Benjamin LaHaise wrote: > Is it possible to get an optimization for this case where uml can execute > the kernel thread in the same process as it normally executes kernel mode > for the given mm? AIO performance on uml is pretty bad when it has to > access userspace. I thought to another solution to that, i.e. use get_user_pages() and kmap() the resulting pages, like other kernel threads do when accessing userspace context.
However, by looking at the code (starting from aio_pread), maybe AIO reuses too much normal I/O code to do this.
Actually, the changes wouldn't maybe be so intrusive, they're limited to __generic_file_aio_read (conditionalize access_ok, and change the setup of read_descriptor_t) and file_read_actor, plus the write side, plus anything not using pagecache - generic_file_aio_read.
Having a different actor for AIO would work. The real problem is adding a field to iovec to specify whether we're passing in a page array (given by get_user_pages) rather than a void __user *, or passing an iovec "wrapper" structure, which can carry either a normal iovec or the new kind of descriptor.
However, this does not sound like too much added complexity. Instead, allowing to move a kernel thread elsewhere on the host is a lot more difficult. -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade
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