linux-kernel - Re: [PATCH 1/2] net: thunderx: Set recevie buffer page usage count in bulk

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Message-ID: <CA+sq2CewOQGSiRC5m64ioYS36-WO0C5XzykZRZd+OLE1tJ-sSQ@mail.gmail.com>
Date:	Mon, 7 Mar 2016 22:28:39 +0530
From:	Sunil Kovvuri <sunil.kovvuri@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Linux Netdev List <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	Sunil Goutham <sgoutham@...ium.com>,
	Robert Richter <robert.richter@...iumnetworks.com>
Subject: Re: [PATCH 1/2] net: thunderx: Set recevie buffer page usage count in bulk

Hi David,

>> you create a window of time during which the consumer
>> can release the page and prematurely free it.
Okay, but here the consumer i.e HW is notified only after page count
is incremented.
For example if you check 'nicvf_refill_rbdr' fn() only after receive
buffer ring is
refilled with buffers, doorbell is issued to hardware to start using
the new buffers.

So
@@ -241,6 +254,8 @@ refill:
                new_rb++;
        }

+       nicvf_get_page(nic);
+
calling 'nicvf_get_page' before issuing doorbell ensures page ref
count is properly
set before hw/consumer can use the buffers.

Thanks,
Sunil.