Re: Cygwin speed

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

On Wed, Mar 07, 2007 at 09:13:33PM +0100, Christian Franke wrote:
>Christopher Layne wrote:
>>On Fri, Mar 02, 2007 at 11:11:54AM -0800, Brian Dessent wrote:
>>>Vinod Gupta wrote:
>>>
>>>>Cygwin was a slow by a factor of 3x. Is that normal?
>>>Yes.  Emulation of POSIX functions which do not exist on Windows is
>>>expensive.  Fork is especially bad, which is all you're really testing
>>>there.
>>
>>Where is the *continual* fork in his script btw?
>
>There is no fork at all, the script uses only builtin shell commands.
>
>This command prints the fork() count of a script on Cygwin:
>
>$ strace bash ./script.sh | grep -c 'fork: 0 = fork()'
>
>
>One reason for the slow execution of the script are >8000000 context 
>switches done by Cygwin.
>
>Bash calls sigprocmask() before starting each command, even for builtin 
>commands.
>Cygwin's sigprocmask() unconditionally calls sig_dispatch_pending().
>This is necessary because POSIX requires that at least one pending 
>signal is dispatched by sigprocmask().
>sig_dispatch_pending() sends a __SIGFLUSH* to self and this causes 2 
>thread context switches: main->sig->main.
>
>With the attached patch, sigprocmask() does nothing if the signal mask 
>is not changed.
>This reduces the context switches to <5000.
>(Patch is only intended for testing, it at least breaks above POSIX rule)

I removed the sig_dispatch_pending from handle_sigprocmask.  I don't see
any need for extra logic beyond that since you're doing tests that are
already being done in set_signal_mask.

I'll generate a snapshot with these changes for testing.

Thanks for the patch.

cgf

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