netdev - Re: [RFC net-next 5/5] eventpoll: Control irq suspension for prefer_busy

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]

Message-ID: <9b3d8ad0-7e91-4b9d-9ffe-b11c10e7344f@uwaterloo.ca>
Date: Mon, 12 Aug 2024 17:47:10 -0400
From: Martin Karsten <mkarsten@...terloo.ca>
To: Stanislav Fomichev <sdf@...ichev.me>
Cc: netdev@...r.kernel.org, Joe Damato <jdamato@...tly.com>,
 amritha.nambiar@...el.com, sridhar.samudrala@...el.com,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 "open list:FILESYSTEMS (VFS and infrastructure)"
 <linux-fsdevel@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next 5/5] eventpoll: Control irq suspension for
 prefer_busy_poll

On 2024-08-12 16:20, Stanislav Fomichev wrote:
> On 08/12, Joe Damato wrote:
>> From: Martin Karsten <mkarsten@...terloo.ca>

[snip]

>> @@ -2005,8 +2023,10 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
>>   			 * trying again in search of more luck.
>>   			 */
>>   			res = ep_send_events(ep, events, maxevents);
>> -			if (res)
>> +			if (res) {
>> +				ep_suspend_napi_irqs(ep);
> 
> Aren't we already doing defer in the busy_poll_stop? (or in napi_poll
> when it's complete/done). Why do we need another rearming here?

If ep_poll finds data present due to previous softirq activity during a 
sleep (or application bootstrap), the timer is armed with the shorter 
gro-flush-timeout. This timer rearming with irq-suspend-timeout 
kickstarts the suspend mechanism by injecting the larger timer.

Thanks,
Martin