Hacking on the rtl8366S

[Dave Taht]

So I built a fresh build of openwrt from git head, patched in my preliminary
patch to the switch, compiled it with oprofile support, and turned on -O2
rather than -Os, in my usual approach to all-up testing that makes it hard
to track down what's really going on without backtracking.

The net result with iperf was better than before,
with iptables and qos turned entirely off, no nat, etc.
pings stayed very flat and well below 8ms, down from 100ms.

elara: [  3]  0.0-60.0 sec   435 MBytes  60.7 Mbits/sec
io: [  3]  0.0-60.0 sec   495 MBytes  69.2 Mbits/sec
leda: [  3]  0.0-60.9 sec   226 MBytes  31.1 Mbits/sec
thebe: [  3]  0.0-60.0 sec   105 MBytes  14.7 Mbits/sec

(how all this stuff is routed is beyond the scope of this, but only
partially explains the discrepancies above)

Oprofiling a later run, we're spending a lot of time in an unaligned trap,
and I have no idea why iptables and conntrack even register.

I am not sure at the moment how to track down the source of the alignment
fault, I assume I can look at the performance counter somehow, and backtrack
that to a given function or functions. It's late...

samples  cum. samples  %        cum. %     app name                 symbol
name
14992    14992         22.7158  22.7158    vmlinux                  do_ade
10054    25046         15.2338  37.9496    ip_tables
/ip_tables
7257     32303         10.9958  48.9454    nf_conntrack
/nf_conntrack
3398     35701          5.1486  54.0941    vmlinux
handle_adel_int
2613     38314          3.9592  58.0533    vmlinux                  ip_rcv
2356     40670          3.5698  61.6231    vmlinux
nf_iterate
1869     42539          2.8319  64.4550    iptable_nat
/iptable_nat
1626     44165          2.4637  66.9187    vmlinux
r4k_dma_cache_inv
1544     45709          2.3395  69.2582    nf_conntrack_ipv4
/nf_conntrack_ipv4
1331     47040          2.0167  71.2749    vmlinux
ag71xx_poll
1011     48051          1.5319  72.8068    vmlinux
ip_route_input_common
988      49039          1.4970  74.3038    vmlinux
ret_from_exception



asmlinkage void do_ade(struct pt_regs *regs)
{
        unsigned int __user *pc;
        mm_segment_t seg;

        perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS,
                        1, 0, regs, regs->cp0_badvaddr);
        /*
         * Did we catch a fault trying to load an instruction?
         * Or are we running in MIPS16 mode?
         */
        if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
                goto sigbus;

        pc = (unsigned int __user *) exception_epc(regs);
        if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
                goto sigbus;
        if (unaligned_action == UNALIGNED_ACTION_SIGNAL)
                goto sigbus;
        else if (unaligned_action == UNALIGNED_ACTION_SHOW)
                show_registers(regs);

        /*
         * Do branch emulation only if we didn't forward the exception.
         * This is all so but ugly ...
         */
        seg = get_fs();
        if (!user_mode(regs))
                set_fs(KERNEL_DS);
        emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr,
pc);
        set_fs(seg);

        return;


-- 
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://the-edge.blogspot.com
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