Messages in this thread | | | Date | Thu, 3 Feb 2022 17:56:16 +0100 | From | Miquel Raynal <> | Subject | Re: [RFC PATCH] mtd: tests: Fix eraseblock read speed miscalculation for lower partition sizes |
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Hi Amit,
+Cc: David, who's maintaining the tools. Please keep him in the recipients list!
amit.kumar-mahapatra@xilinx.com wrote on Thu, 3 Feb 2022 18:54:34 +0530:
> While calculating speed during mtd_speedtest, the time interval > (i.e., start - finish) is rounded off to the nearest milliseconds by > ignoring the fractional part. This leads to miscalculation of speed. > The miscalculation is more visible while running speed test on small > partition sizes(i.e., when partition size is equal to eraseblock size or > twice the eraseblock size) at higher spi frequencies. > > For e.g., while calculating eraseblock read speed for a mtd partition with > size equal to the eraseblock size(i.e., 64KiB) the eraseblock read time > interval comes out to be 966490 nanosecond. This is then converted to > millisecond(i.e., 0.966 msec.). The integer part (i.e., 0 msec) of the > value is considered and the fractional part (i.e., 0.966) is ignored,for > calculating the eraseblock read speed. So the reported eraseblock read > speed is 0 KiB/s, which is incorrect. > > There are two approaches to fix this issue. > > First approach will be to keep the time interval in millisecond. and round > up the integer value, with this approach the 0.966msec time interval in the > above example will be rounded up to 1msec and this value is used for > calculating the speed. Downside of this approach is that the reported speed > is still not accurate. > > Second approach will be to convert the time interval to microseconds > instead of milliseconds, with this approach the 966490 nanosecond time > interval in the above example will be converted t0 966.490usec and this > value is used for calculating the speed. As compared to the current > implementation and the suggested First approach, this approach will report > a more accurate speed. Downside of this approach is that, in future if the > mtd size is too large then the u64 variable, that holds the number of > bytes, might overflow. > > In this patch we have gone with the second approach as this reports a more > accurate speed. With this approach the eraseblock read speed in the above > example comes out to be 132505 KiB/s when the spi clock is configured at > 150Mhz. > > Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com> > --- > BRANCH: mtd/next > --- > drivers/mtd/tests/speedtest.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/drivers/mtd/tests/speedtest.c b/drivers/mtd/tests/speedtest.c > index 93e76648f676..2b76e7750c68 100644 > --- a/drivers/mtd/tests/speedtest.c > +++ b/drivers/mtd/tests/speedtest.c > @@ -161,13 +161,13 @@ static inline void stop_timing(void) > static long calc_speed(void) > { > uint64_t k; > - long ms; > + long us;
Should this be an explicit 64-bit value? And unsigned? unsigned long long int or uint64_t? I believe we are now 1000x closer to the 4GiB limit so we might need to enlarge this variable.
> > - ms = ktime_ms_delta(finish, start); > - if (ms == 0) > + us = ktime_us_delta(finish, start); > + if (us == 0) > return 0; > - k = (uint64_t)goodebcnt * (mtd->erasesize / 1024) * 1000; > - do_div(k, ms); > + k = (uint64_t)goodebcnt * (mtd->erasesize / 1024) * 1000000; > + do_div(k, us); > return k; > } >
Otherwise lgtm!
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Thanks, Miquèl
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