Date: Wed, 10 Feb 2016 00:26:24 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 207068] hwpmc wrap around/sign extension Message-ID: <bug-207068-8@https.bugs.freebsd.org/bugzilla/>
next in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D207068 Bug ID: 207068 Summary: hwpmc wrap around/sign extension Product: Base System Version: 10.2-STABLE Hardware: amd64 OS: Any Status: New Keywords: hwpmc Severity: Affects Some People Priority: --- Component: kern Assignee: freebsd-bugs@FreeBSD.org Reporter: joss.upton@yahoo.com CC: freebsd-amd64@FreeBSD.org, joss.upton@yahoo.com CC: freebsd-amd64@FreeBSD.org hwpmc_intel writes the old value of a counter back to the counter value register during a context switch in. However, those registers ignore the u= pper 32 bits (EDX) and instead sign extended to the register width based on EAX[= 31]. This is the behavior on all machines not supporting "full width writes" (indicated by CPUID2_PDCM being set && and IA32_PERF_CAPABILITIES(0x345) & FW_WRITE(bit 13) being set). If full width writes are supported, full-width aliases for IA32_PMCn exist 0x400 MSRs higher (e.g. IA32_PMC0 =3D=3D 0xC1 and IA32_A_PMC0 =3D 0x4C1). This affects processes monitoring CPU_CLK for processes running more than a second or two. Using this counter quickly runs into a "negative increment" assertion in hwpmc_mod.c because of the sign extension. Attached is the le= ast invasive patch I could come up with and it's against 10.2-R. It also fixes a few debugging PMCDBGs and adjusts the size of PMC_DEFAULT_DEBUG_FLAGS to match the size of the structure. --=20 You are receiving this mail because: You are the assignee for the bug.=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-207068-8>