linux-kernel - Re: [PATCH] poll: Avoid extra wakeups in select/poll

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Date:	Tue, 28 Apr 2009 22:05:08 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	linux kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>, jesse.brandeburg@...el.com,
	netdev@...r.kernel.org, haoki@...hat.com, mchan@...adcom.com,
	davidel@...ilserver.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] poll: Avoid extra wakeups in select/poll

Christoph Lameter a écrit :
> For the udpping test load these patches have barely any effect:
> 
> git2p1 is the first version of the patch
> git2p2 is the second version (this one)

But... udpping does *not* use poll() nor select(), unless I am mistaken ?

If you really want to test this patch with udpping, you might add a poll() call
before recvfrom() :

                while(1) {
+                       struct pollfd pfd = { .fd = sock, .events = POLLIN};
+                       poll(pfd, 1, -1);
                        nbytes = recvfrom(sock, msg, min(inblocksize, sizeof(msg)),
                                                                0, &inad, &inadlen);
                        if (nbytes < 0) {
                                perror("recvfrom");
                                break;
                        }
                        if (sendto(sock, msg, nbytes, 0, &inad, inadlen) < 0) {
                                perror("sendto");
                                break;
                        }
                }

Part about recvfrom() wakeup avoidance is in David net-2.6 tree, and saves 2 us on udpping here.

Is it what you call git2p1 ?



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