Date: Fri, 18 Mar 2016 19:48:49 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r297039 - head/sys/x86/x86 Message-ID: <201603181948.u2IJmndg063765@repo.freebsd.org>
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Author: jhb Date: Fri Mar 18 19:48:49 2016 New Revision: 297039 URL: https://svnweb.freebsd.org/changeset/base/297039 Log: Check IPI status more frequently when waiting. An IPI cannot be sent via the local APIC if a previous IPI is still being delivered. Attempts to send an IPI will wait for a pending IPI to clear. Prior to r278325 these checks used a spin loop with a hardcoded maximum count which broke AP startup on some systems. However, r278325 also enforced a minimum latency of 5 microseconds if an IPI was still pending which resulted in a measurable performance hit. This change reduces that minimum latency to 1 microsecond. Tested by: stas MFC after: 3 days Modified: head/sys/x86/x86/local_apic.c Modified: head/sys/x86/x86/local_apic.c ============================================================================== --- head/sys/x86/x86/local_apic.c Fri Mar 18 19:36:43 2016 (r297038) +++ head/sys/x86/x86/local_apic.c Fri Mar 18 19:48:49 2016 (r297039) @@ -1641,11 +1641,11 @@ native_lapic_ipi_wait(int delay) return (1); } - for (x = 0; x < delay; x += 5) { + for (x = 0; x < delay; x++) { if ((lapic_read_icr_lo() & APIC_DELSTAT_MASK) == APIC_DELSTAT_IDLE) return (1); - DELAY(5); + DELAY(1); } return (0); }
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