Here are some numbers:

./netperf -l 60 -H gw -t TCP_STREAM -i 10,2 -I 99,5 -- -m 4096 -s 57344
-S 57344

TCP STREAM TEST to gw : +/-2.5% @ 99% conf.

async-ipsec, 10^6bits/sec:  35.42
 sync-ipsec, 10^6bits/sec:  37.11

So even with existing timer deferring it is not noticebly slower [about
4%].

And I think that benefits it provides definitely cost that price and 
compile time option.

-- 
        Evgeniy Polyakov

Crash is better than data corruption -- Arthur Grabowski