The patch titled calibrate: retry with wider bounds when converge seems to fail has been removed from the -mm tree. Its filename was calibrate-retry-with-wider-bounds-when-converge-seems-to-fail.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: calibrate: retry with wider bounds when converge seems to fail From: Phil Carmody <ext-phil.2.carmody@xxxxxxxxx> Systems with unmaskable interrupts such as SMIs may massively underestimate loops_per_jiffy, and fail to converge anywhere near the real value. A case seen on x86_64 was an initial estimate of 256<<12, which converged to 511<<12 where the real value should have been over 630<<12. This admitedly requires bypassing the TSC calibration (lpj_fine), and a failure to settle in the direct calibration too, but is physically possible. This failure does not depend on my previous calibration optimisation, but by luck is easy to fix with the optimisation in place with a trivial retry loop. In the context of the optimised converging method, as we can no longer trust the starting estimate, enlarge the search bounds exponentially so that the number of retries is logarithmically bounded. [akpm@xxxxxxxxxxxxxxxxxxxx: mention x86_64 SMIs in comment] Signed-off-by: Phil Carmody <ext-phil.2.carmody@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Tested-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx> Cc: Greg KH <greg@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- init/calibrate.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff -puN init/calibrate.c~calibrate-retry-with-wider-bounds-when-converge-seems-to-fail init/calibrate.c --- a/init/calibrate.c~calibrate-retry-with-wider-bounds-when-converge-seems-to-fail +++ a/init/calibrate.c @@ -122,7 +122,7 @@ static unsigned long __cpuinit calibrate static unsigned long __cpuinit calibrate_delay_converge(void) { /* First stage - slowly accelerate to find initial bounds */ - unsigned long lpj, ticks, loopadd, chop_limit; + unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit; int trials = 0, band = 0, trial_in_band = 0; lpj = (1<<12); @@ -146,14 +146,18 @@ static unsigned long __cpuinit calibrate * the largest likely undershoot. This defines our chop bounds. */ trials -= band; - loopadd = lpj * band; - lpj *= trials; - chop_limit = lpj >> (LPS_PREC + 1); + loopadd_base = lpj * band; + lpj_base = lpj * trials; + +recalibrate: + lpj = lpj_base; + loopadd = loopadd_base; /* * Do a binary approximation to get lpj set to * equal one clock (up to LPS_PREC bits) */ + chop_limit = lpj >> LPS_PREC; while (loopadd > chop_limit) { lpj += loopadd; ticks = jiffies; @@ -165,6 +169,16 @@ static unsigned long __cpuinit calibrate lpj -= loopadd; loopadd >>= 1; } + /* + * If we incremented every single time possible, presume we've + * massively underestimated initially, and retry with a higher + * start, and larger range. (Only seen on x86_64, due to SMIs) + */ + if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) { + lpj_base = lpj; + loopadd_base <<= 2; + goto recalibrate; + } return lpj; } _ Patches currently in -mm which might be from ext-phil.2.carmody@xxxxxxxxx are origin.patch linux-next.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html