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Date: Tue, 21 Mar 1995 15:21:45 +0900
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To: bde@zeta.org.au
Cc: current@FreeBSD.org, se@MI.Uni-Koeln.DE
Subject: Re: Sharing interrupts with PCI devices?
In-Reply-To: <199503210529.PAA04875@godzilla.zeta.org.au>
From: =?ISO-2022-JP?B?GyRCQjwwZhsoSg==?= 
	=?ISO-2022-JP?B?GyRCPV8bKEo=?= Atsushi Murai  <amurai@spec.co.jp>
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Bruce Evans <bde@zeta.org.au> wrotes:
>>This results in low overhead operation 
>>in the non shared case, and in interrupts
>>masked for as short a period of time as
>>possible in the shared case.
>
>>*** *** *** *** *** *** *** *** *** *** ***
>
>>I will apply the PCI SHARED INTERRUPT patch
>>tomorrow. All PCI device drivers will have 
>>been checked to conform to the return value 
>>convention described above !
>
>This results in a higher overhead operation
>in the non-shared case :-].  What about
>generic drivers like isa/bt742a.c?  Does
>the new requirement give higher overhead
>in the non-shared ISA (VLB) case?
>
>The overheads are relatively _very_ small for
>devices that transfer large blocks so I'm not
>worried about the overheads for bt742a.

Case 1: Sharing same IRQ by same device.   
 Consider with for EISA, This is using sharing interruption by level sense.
 This mean once interrupter ocurred, another interrupter never interrupt
 for Interrupt controler during procees a same device interrupt service
 for card. And obiously, a device interruption routine should know their 
 sharing interrupiton group and I/O chanels. Thus it's could be reduce
 number of interrupt even checking validation by reading extra I/O port.
 So it will give us decreas overhead under the heavy load for these device.

Case 2: Sharing same IRQ by different device.
 This case, System interrupt service routine should dispatch and poll 
 for any same interrupt for which different devices are configred. 
 But this is only useful for limited of IRQ resouse situation.

>Bruce

Atsushi.

-- 
Atsushi Murai                                         E-Mail: amurai@spec.co.jp
SPEC                                                  Voice : +81-3-3833-5341
System Planning and Engineering Corp.