On Sat, 2017-04-15 at 13:07 -0400, Jamal Hadi Salim wrote: > Eric, > > How does attached look instead of the 32K? > I found it helps to let user space suggest something > larger. > > cheers, > jamal
Looks dangerous to me, for various reasons. 1) Memory allocations might not like it Have you tried your change after user does a setsockopt( SO_RCVBUFFORCE, 256 Mbytes), and a recvmsg ( .. 64 Mbytes) ? Presumably, we could replace 32768 by (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER), but this will not matter on x86. 2) We might have paths in the kernel filling a potential big skb without yielding cpu or a spinlock or a mutex. -> latency source. What perf numbers do you have, using 1MB buffers instead of 32KB ? The syscall overhead seems tiny compared to the actual cost of filling the netlink message, accessing thousands of cache lines all over the places.
