From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH 2/2] random32: use msecs_to_jiffies for reseed timer Date: Tue, 12 Nov 2013 15:35:12 -0800 Message-ID: <20131112153512.68520cca@samsung-9> References: <1384296342-3348-1-git-send-email-dborkman@redhat.com> <1384296342-3348-2-git-send-email-dborkman@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org, Hannes Frederic Sowa To: Daniel Borkmann Return-path: Received: from mail-pd0-f172.google.com ([209.85.192.172]:43641 "EHLO mail-pd0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756319Ab3KLXfU (ORCPT ); Tue, 12 Nov 2013 18:35:20 -0500 Received: by mail-pd0-f172.google.com with SMTP id w10so7608380pde.31 for ; Tue, 12 Nov 2013 15:35:19 -0800 (PST) In-Reply-To: <1384296342-3348-2-git-send-email-dborkman@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 12 Nov 2013 23:45:42 +0100 Daniel Borkmann wrote: > Use msecs_to_jiffies, for these calculations as different HZ > considerations are taken into account for conversion of the timer > shot, and also it makes the code more readable. > > Signed-off-by: Daniel Borkmann > Signed-off-by: Hannes Frederic Sowa > --- > lib/random32.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/lib/random32.c b/lib/random32.c > index 4f9d5df..1e5b2df 100644 > --- a/lib/random32.c > +++ b/lib/random32.c > @@ -214,18 +214,22 @@ static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0); > static void __prandom_timer(unsigned long dontcare) > { > u32 entropy; > + unsigned long expires; > > get_random_bytes(&entropy, sizeof(entropy)); > prandom_seed(entropy); > + > /* reseed every ~60 seconds, in [40 .. 80) interval with slack */ > - seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ))); > + expires = 40 + (prandom_u32() % 40); > + seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC); > + > add_timer(&seed_timer); > } > > static void __init __prandom_start_seed_timer(void) > { > set_timer_slack(&seed_timer, HZ); > - seed_timer.expires = jiffies + 40 * HZ; > + seed_timer.expires = jiffies + msecs_to_jiffies(40 * MSEC_PER_SEC); > add_timer(&seed_timer); > } > Some questions: 1. What is the point of using msecs_to_jiffies? the older code already handled differing HZ? 2. Why the magic 40-80 sec range? What about platforms with very low entropy you will end up draining it faster. 3. I prefer using mod_timer rather than setting expires and call add_timer 4. You should also use round_jiffies to save power by making the wakeup on a second boundary.