Re: Route cache performance under stress

[Ralph Doncaster <ralph@xxxxxxxxx>]

On Tue, 10 Jun 2003, David S. Miller wrote:

> TSC do_gettimeofday() is REALLY cheap (TSC read plus a multiply which
> x86 does in like 5 cycles).

Aren't the read_lock_irqsave and restore expensive?

        read_lock_irqsave(&xtime_lock, flags);
        usec = do_gettimeoffset();
        {
                unsigned long lost = jiffies - wall_jiffies;
                if (lost)
                        usec += lost * (1000000 / HZ);
        }
        sec = xtime.tv_sec;
        usec += xtime.tv_usec;
        read_unlock_irqrestore(&xtime_lock, flags);