Messages in this thread | | | Subject | Re: [Patch] Fix sys_time to handle intra-tick correction | From | john stultz <> | Date | Tue, 09 Dec 2008 16:24:27 -0800 |
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On Tue, 2008-12-09 at 17:28 +0530, Vinay Sridhar wrote: > Hi All, > > This fix changes sys_time to use do_gettimeofday instead of get_seconds. > Running the stime01 test from LTP triggers this error. Calling sys_stime > and then calling sys_time causes this. "do_settimeofday" subtracts the > nsec offset from the nsec value(0 in this case) passed to it. > Subsequently, "set_normalized_timespec" modifies sec and nsec > accordingly. This compensation is handled in the do_gettimeofday path. > However, sys_time does not handle this case and reports an incorrect > seconds value. > > > signed-off by : Vinay Sridhar <vinay@linux.vnet.ibm.com>
This does fix the symmetry by using the same interfaces on both sides, so it seems reasonable to me. However, since do_gettimeofday reads the clocksource hardware, this may have a slight performance impact to time() users.
I know privately I said this patch looked fine earlier, so sorry for the mixed messages, but I really think we should be able to use get_seconds() without this problem.
Looking more carefully at the code in do_settimeofday(), we should accumulate the left over cycles, then we set the current time to the specified time and update the xtime_cache.
So I'm not sure if we're really fixing the right issue here. Further, running on the x86_64 system, I don't see this issue crop up at all (for either 64 or 32 bit binaries). I think you mentioned privately that this was seen on i386, so maybe we need to dig just a bit deeper before going with this fix.
And sorry again for running hot then cold on this patch. I just didn't look deeply enough at the issue the first time around. :(
thanks -john
> --- time.c.orig 2008-12-04 06:30:12.000000000 -0600 > +++ time.c 2008-12-04 06:31:25.000000000 -0600 > @@ -61,7 +61,12 @@ EXPORT_SYMBOL(sys_tz); > */ > asmlinkage long sys_time(time_t __user * tloc) > { > - time_t i = get_seconds(); > + struct timeval t; > + time_t i; > + > + do_gettimeofday(&t); > + > + i = t.tv_sec; > > if (tloc) { > if (put_user(i,tloc)) > >
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