Hi,

This patchset tries to optimize ebpf hash map, and follows
the idea:

	Both htab_map_update_elem() and htab_map_delete_elem()
	can be called from eBPF program, and they may be in kernel
	hot path, it isn't efficient to use a per-hashtable lock
	in this two helpers, so this patch converts the lock into
	per-bucket spinlock.

With this patchset, looks the performance penalty from eBPF
decreased a lot, see the following test:

	1) run 'tools/biolatency' of bcc before running block test;

	2) run fio to test block throught over /dev/nullb0,
	(randread, 16jobs, libaio, 4k bs) and the test box
	is one 24cores(dual sockets) VM server:
        - without patchset:  607K IOPS
        - with this patchset: 1184K IOPS
        - without running eBPF prog: 1492K IOPS

TODO:
	- remove the per-hashtable atomic counter 

 kernel/bpf/hashtab.c | 49 +++++++++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 18 deletions(-)

thanks,
Ming