Date: Fri, 08 Apr 2011 13:23:29 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: svn-src-head@FreeBSD.org, FreeBSD-Current <freebsd-current@FreeBSD.org>, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r220430 - head/sys/amd64/amd64 Message-ID: <4D9EE221.40200@FreeBSD.org> In-Reply-To: <201104072132.p37LWPuu052536@svn.freebsd.org> References: <201104072132.p37LWPuu052536@svn.freebsd.org>
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on 08/04/2011 00:32 John Baldwin said the following: > Author: jhb > Date: Thu Apr 7 21:32:25 2011 > New Revision: 220430 > URL: http://svn.freebsd.org/changeset/base/220430 > > Log: > If a system call does not request a full interrupt return, use a fast > path via the sysretq instruction to return from the system call. This was > removed in 190620 and not quite fully restored in 195486. This resolves > most of the performance regression in system call microbenchmarks between > 7 and 8 on amd64. > > Reviewed by: kib > MFC after: 1 week I think that this commit (plus r220431) has broken something in my environment. After updating to the most recent head I started to get semi-random problems in various areas: - named would consistently fail to start, but with different errors (assertions) - ^Z and fg result in a process getting SIGSEGV - X sometimes fails to start complaining about failed VT switch Reverting just these two commits restores sanity. Just in case, my processor is AMD (arch is obviously amd64). > Modified: > head/sys/amd64/amd64/exception.S > > Modified: head/sys/amd64/amd64/exception.S > ============================================================================== > --- head/sys/amd64/amd64/exception.S Thu Apr 7 21:29:34 2011 (r220429) > +++ head/sys/amd64/amd64/exception.S Thu Apr 7 21:32:25 2011 (r220430) > @@ -339,6 +339,9 @@ IDTVEC(prot) > * and the new privilige level. We are still running on the old user stack > * pointer. We have to juggle a few things around to find our stack etc. > * swapgs gives us access to our PCPU space only. > + * > + * We do not support invoking this from a custom %cs or %ss (e.g. using > + * entries from an LDT). > */ > IDTVEC(fast_syscall) > swapgs > @@ -380,6 +383,36 @@ IDTVEC(fast_syscall) > movq %rsp,%rdi > call syscall > movq PCPU(CURPCB),%rax > + testq $PCB_FULL_IRET,PCB_FLAGS(%rax) > + jne 3f > +1: /* Check for and handle AST's on return to userland. */ > + cli > + movq PCPU(CURTHREAD),%rax > + testl $TDF_ASTPENDING | TDF_NEEDRESCHED,TD_FLAGS(%rax) > + je 2f > + sti > + movq %rsp, %rdi > + call ast > + jmp 1b > +2: /* Restore preserved registers. */ > + MEXITCOUNT > + movq TF_RDI(%rsp),%rdi /* bonus; preserve arg 1 */ > + movq TF_RSI(%rsp),%rsi /* bonus: preserve arg 2 */ > + movq TF_RDX(%rsp),%rdx /* return value 2 */ > + movq TF_RAX(%rsp),%rax /* return value 1 */ > + movq TF_RBX(%rsp),%rbx /* C preserved */ > + movq TF_RBP(%rsp),%rbp /* C preserved */ > + movq TF_R12(%rsp),%r12 /* C preserved */ > + movq TF_R13(%rsp),%r13 /* C preserved */ > + movq TF_R14(%rsp),%r14 /* C preserved */ > + movq TF_R15(%rsp),%r15 /* C preserved */ > + movq TF_RFLAGS(%rsp),%r11 /* original %rflags */ > + movq TF_RIP(%rsp),%rcx /* original %rip */ > + movq TF_RSP(%rsp),%r9 /* user stack pointer */ > + movq %r9,%rsp /* original %rsp */ > + swapgs > + sysretq > +3: /* Requested full context restore, use doreti for that. */ > MEXITCOUNT > jmp doreti > -- Andriy Gapon
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