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In both cases, the the effect of the bug was that a very small positive number was written to the counter. This means that a large number of events needed to occur before the next sampling interrupt would trigger. Even with very frequently occurring events like clock cycles wrapping all the way around could take a long time. Both bugs occurred when updating the saved reload count for an outgoing thread on a context switch. First, the counter-independent code compares the current reload count against the count set when the thread switched in and generates a delta to apply to the saved count. If this delta causes the reload counter to go negative, it would add a full reload interval to wrap it around to a positive value. The fix is to add the full reload interval if the resulting counter is zero. Second, occasionally the raw counter value read during a context switch has actually wrapped, but an interrupt has not yet triggered. In this case the existing logic would return a very large reload count (e.g. 2^48 - 2 if the counter had overflowed by a count of 2). This was seen both for fixed-function and programmable counters on an E5-2643. Workaround this case by returning a reload count of zero. PR: 198149 Differential Revision: https://reviews.freebsd.org/D2557 Reviewed by: emaste MFC after: 1 week Sponsored by: Norse Corp, Inc. |
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| .. | ||
| hwpmc_amd.c | ||
| hwpmc_amd.h | ||
| hwpmc_arm64_md.c | ||
| hwpmc_arm64.c | ||
| hwpmc_arm64.h | ||
| hwpmc_arm.c | ||
| hwpmc_armv7.c | ||
| hwpmc_armv7.h | ||
| hwpmc_core.c | ||
| hwpmc_core.h | ||
| hwpmc_e500.c | ||
| hwpmc_intel.c | ||
| hwpmc_logging.c | ||
| hwpmc_mips24k.c | ||
| hwpmc_mips74k.c | ||
| hwpmc_mips.c | ||
| hwpmc_mod.c | ||
| hwpmc_mpc7xxx.c | ||
| hwpmc_octeon.c | ||
| hwpmc_pentium.c | ||
| hwpmc_pentium.h | ||
| hwpmc_piv.c | ||
| hwpmc_piv.h | ||
| hwpmc_powerpc.c | ||
| hwpmc_powerpc.h | ||
| hwpmc_ppc970.c | ||
| hwpmc_ppro.c | ||
| hwpmc_ppro.h | ||
| hwpmc_soft.c | ||
| hwpmc_soft.h | ||
| hwpmc_sparc64.c | ||
| hwpmc_tsc.c | ||
| hwpmc_tsc.h | ||
| hwpmc_uncore.c | ||
| hwpmc_uncore.h | ||
| hwpmc_x86.c | ||
| hwpmc_xscale.c | ||
| hwpmc_xscale.h | ||
| pmc_events.h | ||