netdev - Re: RFC: Nagle latency tuning

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 9 Sep 2008 12:54:31 -0400
From:	Chuck Lever <chuck.lever@...cle.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	Chris Snook <csnook@...hat.com>, Netdev <netdev@...r.kernel.org>
Subject: Re: RFC: Nagle latency tuning

On Sep 9, 2008, at Sep 9, 2008, 12:33 PM, Rick Jones wrote:
>> Most of the apps where people care about this enough to complain to  
>> their vendor (the cases I hear about) are in messaging apps, where  
>> they're relaying a stream of events that have little to do with  
>> each other, and they want TCP to maintain the integrity of the  
>> connection and do a modicum of bandwidth management, but 40 ms  
>> stalls greatly exceed their latency tolerances.
>
> What _are_ their latency tolerances?  How often are they willing to  
> tolerate a modicum of TCP bandwidth management?  Do they go ape when  
> TCP sits waiting not just for 40ms, but for an entire RTO timer?
>
>> Using TCP_NODELAY is often the least bad option, but sometimes it's
>> infeasible because of its effect on the network, and it certainly
>> adds to the network stack overhead.  A more tunable Nagle delay would
>> probably serve many of these apps much better.
>
> If the applications are sending streams of logically unrelated sends  
> down the same socket, then setting TCP_NODELAY is IMO fine.  Where  
> it isn't fine is where these applications are generating their  
> logically associated data in two or more small sends.  One send per  
> message good. Two sends per message bad.

Can the same be said of the Linux kernel's RPC client, which uses  
MSG_MORE and multiple sends to construct a single RPC request on a TCP  
socket?

See net/sunrpc/xprtsock.c:xs_send_pagedata() for details.

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html