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    SubjectRe: sched_clock - microblaze
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    On Thu, 2010-04-15 at 18:32 +0200, Michal Simek wrote:
    > Steven Rostedt wrote:
    > > On Thu, 2010-04-15 at 16:55 +0200, Michal Simek wrote:
    > >> Hi Thomas and Steven,
    > >>
    > >> I would like to improve time measuring for ftrace (Log below)
    > >>
    > >> I looked at http://lkml.org/lkml/2009/11/16/181
    > >> where Thomas suggested to create sched_clock() function.
    > >> I used the same solution as Wu proposed but it is not nice.
    > >>
    > >> Is unimplemented sched_clock the reason why ftrace not show fine grain time?
    > >
    > > Yeah, sched_clock is used by ftrace for timings, so if it only returns
    > > jiffies, then that will, unfortunately, be the resolution of the tracer.
    > >
    > > I've been told that if you make a higher resolution timer for sched
    > > clock, it will improve the scheduling in CFS.
    >
    > We have two timers (in one IP).
    > timer0 - in IRQ mode - clock event
    > timer1 - free running up counter without IRQ - clock source
    >
    > I hope that I can use timer1 in sched_clock too.
    >
    > Anyway. I played with it a little bit and I also implemented microblaze
    > specific sched_clock function (inspired by arch/arm/mach-ixp4xx/common.c)
    >
    > unsigned long long notrace sched_clock(void)
    > {
    > printk("%s\n", __func__);
    > cycle_t cyc = microblaze_read(NULL);
    > struct clocksource *cs = &clocksource_microblaze;
    > return clocksource_cyc2ns(cyc, cs->mult, cs->shift);
    > }

    Hey, I guess you got:

    sched_clock() -> printk() -> sched_clock() ...

    since printk() is not annotated with notrace, it will call mcount() and
    then sched_clock() and ... so, you can not call printk() in
    sched_clock().

    but you may try this if you want to print something in sched_clock() for
    debugging.

    #include <>

    sched_clock() {
    ftrace_stop();
    printk(...);
    ftrace_start();
    ...
    }

    Regards,
    Wu Zhangjin

    >
    > (And comment sched_clock in kernel/sched_clock.c because our toolchain
    > has the problem with weak symbols)
    >
    > Recompile the kernel and then show the log_buf
    >
    > <4>Ramdisk addr 0x00000003, Compiled-in FDT at 0xc0242a28
    > <5>Linux version 2.6.34-rc4-00053-gbc6ce8a-dirty (monstr@monstr.eu) (gcc
    > version 4.1.2) #27 Thu Apr 15 16:38:16 CEST 2010
    > <6>setup_cpuinfo: initialising
    > <6>setup_cpuinfo: Using full CPU PVR support
    > <6>cache: wb_msr
    > <6>setup_memory: Main mem: 0x48000000-0x50000000, size 0x08000000,
    > klimit 0xc09c7000
    > <6>setup_memory: max_mapnr: 0x8000
    > <6>setup_memory: min_low_pfn: 0x48000
    > <6>setup_memory: max_low_pfn: 0x50000
    > <4>reserved 0 - 0x48000000-0x009c8000
    > <4>reserved 1 - 0x48fe0000-0x00020000
    > <4>reserved 2 - 0x4fffd8c8-0x00002738
    > <7>On node 0 totalpages: 32768
    > <7>free_area_init_node: node 0, pgdat c02bc70c, node_mem_map c09c8000
    > <7> Normal zone: 256 pages used for memmap
    > <7> Normal zone: 32512 pages, LIFO batch:7
    > <4>Built 1 zonelists in Zone order, mobility grouping on. Total pages:
    > 32512
    > <5>Kernel command line: console=ttyS0,115200
    > <6>PID hash table entries: 512 (order: -1, 2048 bytes)
    > <6>Dentry cache hash table entries: 16384 (order: 4, 65536 bytes)
    > <6>Inode-cache hash table entries: 8192 (order: 3, 32768 bytes)
    > <6>Memory: 119796k/131072k available
    > <4>sched_clock
    >
    > The problem I see is that scheck_clock is used before our timer
    > subsystem is initialized.
    > What am I missing?
    >
    > Thanks,
    > Michal
    >




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