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authorIngo Molnar <mingo@kernel.org>2015-05-18 12:05:13 +0200
committerIngo Molnar <mingo@kernel.org>2015-05-18 12:14:25 +0200
commit7cb685982157567dcc55eb92d1c38d237465203b (patch)
tree35ce1d54ad96cb69d38edb22b9ff41dd72cea8f9 /arch/x86/pci/irq.c
parentMerge branch 'x86/asm' into x86/apic, to resolve conflicts (diff)
downloadlinux-7cb685982157567dcc55eb92d1c38d237465203b.tar.xz
linux-7cb685982157567dcc55eb92d1c38d237465203b.zip
x86/smp/boot: Fix legacy SMP bootup slow-boot bug
So while testing kernels using tools/kvm/ (kvmtool) I noticed that it booted super slow: [ 0.142991] Performance Events: no PMU driver, software events only. [ 0.149265] x86: Booting SMP configuration: [ 0.149765] .... node #0, CPUs: #1 [ 0.148304] kvm-clock: cpu 1, msr 2:1bfe9041, secondary cpu clock [ 10.158813] KVM setup async PF for cpu 1 [ 10.159000] #2 [ 10.159000] kvm-stealtime: cpu 1, msr 211a4d400 [ 10.158829] kvm-clock: cpu 2, msr 2:1bfe9081, secondary cpu clock [ 20.167805] KVM setup async PF for cpu 2 [ 20.168000] #3 [ 20.168000] kvm-stealtime: cpu 2, msr 211a8d400 [ 20.167818] kvm-clock: cpu 3, msr 2:1bfe90c1, secondary cpu clock [ 30.176902] KVM setup async PF for cpu 3 [ 30.177000] #4 [ 30.177000] kvm-stealtime: cpu 3, msr 211acd400 One CPU booted up per 10 seconds. With 120 CPUs that takes a while. Bisection pinpointed this commit: 853b160aaafb ("Revert f5d6a52f5111 ("x86/smpboot: Skip delays during SMP initialization similar to Xen")") But that commit just restores previous behavior, so it cannot cause the problem. After some head scratching it turns out that these two commits: 1a744cb356c5 ("x86/smp/boot: Remove 10ms delay from cpu_up() on modern processors") d68921f9bd14 ("x86/smp/boot: Add cmdline "cpu_init_udelay=N" to specify cpu_up() delay") added the following code to smpboot.c: - mdelay(10); + mdelay(init_udelay); Note the mismatch in the units: the delay is called 'udelay' and is set to microseconds - while the function used here is actually 'mdelay', which counts in milliseconds ... So the delay for legacy systems is off by a factor of 1,000, so instead of 10 msecs we waited for 10 seconds ... The reason bisection pointed to 853b160aaafb was that 853b160aaafb removed a (broken) boot-time speedup patch, which masked the factor 1,000 bug. Fix it by using udelay(). This fixes my bootup problems. Cc: Len Brown <len.brown@intel.com> Cc: Alan Cox <alan@linux.intel.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jan H. Schönherr <jschoenh@amazon.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/pci/irq.c')
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