Hi Ken! On 9 Nov 2006, at 21:21, Ken Hornstein wrote:
I'm not a guru, but I think that's not correct. pread/pwrite are there to prevent some races, not to save time. And at least in Linux syscalls are _fast_, because there is no context switch (that term is reserved for the switch between processes, as that is a _lot_ slower than entering/exiting kernel space). That's the whole point of mapping kernel address space into each vm (with proper protection, of course).Hm, I am wondering if that's a win; that means two extra syscalls.Here two extra syscalls (a few microseconds nowadays?) can save processing a packet (or more), and incurring network latency (a hundred microsecondson my Ether).The syscalls (context switch, a good chunk of cache getting flushed) add up. Why do you think pread() and pwrite() were created? My point was that the extra syscalls may end up killing the advantage you get from sendfile() (the Linux sendfile() ... other sendfiles can add in header data). But ... that's just thinking out loud. Maybe it will be fine.
A syscall is of the order of 1usec, which is much shorter than the network stack latencies which are being talked about in this thread.
Ciao,
Roland
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