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Date: Mon, 18 Nov 2002 14:22:48 -0800
From: "Matthew D. Hall" <mhall@free-market.net>
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To: Davide Libenzi <davidel@xmailserver.org>
CC: Jakub Jelinek <jakub@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Ulrich Drepper <drepper@redhat.com>
Subject: Re: [rfc] epoll interface change and glibc bits ...
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Davide Libenzi wrote:

>On Mon, 18 Nov 2002, Jakub Jelinek wrote:
>
>  
>
>>That is as bad as unsigned long - it is different between 32-bit and 64-bit
>>ABIs.
>>    
>>
>
>Yeah, you right. I did thin about 32bit and 64bit as two diffferent
>kernel-glibc environment, I did not think about 32-64 ABI compatibility.
>Ouch, adding a 64bit object will double the size of the event structure :(
>
>
>
>- Davide
>
>
>
>
>
>-
>To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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>
>  
>
>Yeah, you right. I did thin about 32bit and 64bit as two diffferent
>kernel-glibc environment, I did not think about 32-64 ABI compatibility.
>Ouch, adding a 64bit object will double the size of the event structure :(
>  
>
Pros of a 64-bit opaque user pointer:
- Simpler programming for userland.
- Fewer cache misses, because there is no need for accessing part of a 
separate and large fd->pointer table in userland before being able to 
act upon event notification (some implementations can get around this, 
but it's very common practice).

Cons:
- 4 bytes memory wastage on 32-bit platforms per struct.  Note that it 
is not the full 8, because userland needs to have that table of pointers 
anyway.

Notes:
- No memory wastage for nontrivial applications on 64-bit platforms.

Matthew D. Hall


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