From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Mackall Subject: Nanosecond fs timestamp support: sad Date: Thu, 21 Jul 2011 13:07:21 -0500 Message-ID: <1311271641.14555.114.camel@calx> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit To: linux-fsdevel , Linux Kernel Mailing List Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org So it turns out that the resolution on filesystem timestamps is tied to HZ rather than gettimeofday or similar, which means the resolution improvement over seconds is.. not much. And not nearly as much as advertised! This means I can touch a file something like 70k times per second and get only 300 distinct timestamps on my laptop. And only 100 distinct timestamps on a typical distro server kernel. Meanwhile, I can call gettimeofday 35M times per second and get ~1M distinct responses. Given that we can do gettimeofday three orders of magnitude faster than we can do file transactions and it has four orders of magnitude better resolution, shouldn't we be using it for filesystem time when sb->s_time_gran is less than 1/HZ? -- Mathematics is the supreme nostalgia of our time.