[Lxde-list] LXDE CPU Usage: bug and analysis

[Marko R. <ma...@pa...>]

I have had a recurring LXDE CPU monitor problem: it displays all green
as though the CPU was busy 100% of the time. However, uptime, top etc
indicated everything was fine.

I have now tracked down the root cause in cpu.c (lxpanel-0.5.12.tar.gz)
line 114:

        int fscanf_result = fscanf(stat, "cpu %lu %lu %lu %lu", &cpu.u, &cpu.n, &cpu.s, &cpu.i);

The idle jiffie count has exceeded the unsigned long integer range (my
machine is 32-bit) and instead of wrapping nicely, fscanf() places
ULONG_MAX into the idle counter. That makes LXPanel believe the idle
jiffie count hasn't advanced at all; that is, cpu_delta.i = 0 in:

            c->stats_cpu[c->ring_cursor] = cpu_uns / (cpu_uns + cpu_delta.i);

The simple fix is to specify:

typedef unsigned long long CPUTick;		/* Value from /proc/stat */

and use %llu in fscanf().


Marko