ISAPI Filter call SF_NOTIFY_SEND_RAW_DATA is very slow   

Hi Wade, David,

Is it possible that in IIS 6, the mere registration
SF_NOTIFY_SEND_RAW_DATA in an ISAPI filter will make it slow down
response time?

>From some tests we made, it appears this is the case with IIS 6 (but
not with IIS 5). I realize that some optimizations can't be made when
this event is used, but do you have any information on why it happens
on IIS 6 and not on IIS 5?

thanks
Asaf

date: 21 Feb 2006 11:19:01 -0800   author:   Asaf Dalet

Re: ISAPI Filter call SF_NOTIFY_SEND_RAW_DATA is very slow   

Hi Asaf,

Registering for SF_NOTIFY_SEND_RAW_DATA can definitely affect performance,
particularly for static pages.  The reason for this is that IIS normally
passes a file handle for static pages into kernel mode and lets all of the
IO happen at that layer.  (This functionality is also exposed to ISAPI, so
extensions can optionally use it.)  When you register a SEND_RAW_DATA
filter, IIS has to be able to present the content to the filter.  To do
this, IIS has to do all the work in user mode to read the file data, etc.

From your description, I don't think that this is what's happening, though.
If this were the case, you'd see similar results between IIS 5 and 6, since
they are both affected equally by this.

If you are looking at static file performance, you will see a very dramatic
difference by installing any filter.  The reason for this is that installing
a filter prevents http.sys from being able to cache responses in the kernel.

Also, you should make sure that you are doing your testing on SP1 for IIS 6.
There are a few things that affected the original IIS 6 release that you
could be seeing.  If SP1 does not exhibit the problem, then somehow
registering for SEND_RAW_DATA is somehow causing the issues described in
http://support.microsoft.com/kb/840875/en-us to affect the responses.

I hope that this helps,
-Wade A. Hilmo,
-Microsoft

"Asaf Dalet"  wrote in message
news:1140549541.788635.8740@g44g2000cwa.googlegroups.com...
> Hi Wade, David,
>
> Is it possible that in IIS 6, the mere registration
> SF_NOTIFY_SEND_RAW_DATA in an ISAPI filter will make it slow down
> response time?
>
> >From some tests we made, it appears this is the case with IIS 6 (but
> not with IIS 5). I realize that some optimizations can't be made when
> this event is used, but do you have any information on why it happens
> on IIS 6 and not on IIS 5?
>
> thanks
> Asaf
>

date: Tue, 21 Feb 2006 12:53:58 -0800   author:   Wade A. Hilmo [MS]

Re: ISAPI Filter call SF_NOTIFY_SEND_RAW_DATA is very slow   

thanks Wade.

just to be sure I got you right, you wrote: "If you are looking at
static file performance, you will see a very dramatic difference by
installing any filter."

do you mean ANY filter? even if it only subscribes to, say, the
NOTIFY_LOG event?

thanks again.

Asaf

date: 21 Feb 2006 13:06:20 -0800   author:   Asaf Dalet

Re: ISAPI Filter call SF_NOTIFY_SEND_RAW_DATA is very slow   

Yes. Subscribing to SF_NOTIFY_LOG turns off the kernel response cache in 
IIS6 for those requests.

In general, you can view any "hooks" of ISAPI Filter to hook into IIS 
request processing can disable performance optimizations which in turn 
affect performance characteristics. Static file is one such dramatic case.

-- 
//David
IIS
http://blogs.msdn.com/David.Wang
This posting is provided "AS IS" with no warranties, and confers no rights.
//

"Asaf Dalet"  wrote in message 
news:1140555980.869127.266140@z14g2000cwz.googlegroups.com...
> thanks Wade.
>
> just to be sure I got you right, you wrote: "If you are looking at
> static file performance, you will see a very dramatic difference by
> installing any filter."
>
> do you mean ANY filter? even if it only subscribes to, say, the
> NOTIFY_LOG event?
>
> thanks again.
>
> Asaf
>

date: Tue, 21 Feb 2006 21:21:47 -0800   author:   David Wang [Msft]