Re: svn commit: r220430 - head/sys/amd64/amd64

08.04.2011 14:23, Andriy Gapon пишет:
> 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).
confirm

>> 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)
>> _at__at_ -339,6 +339,9 _at__at_ 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
>> _at__at_ -380,6 +383,36 _at__at_ 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
>>
>