From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from majordomo by infradead.org with local (Exim 3.20 #2) id 14qHWz-0001t1-00 for mtd-list@infradead.org; Thu, 19 Apr 2001 17:43:45 +0100 Message-ID: <3ADF15EF.DBCD9EA@daniel.com> Date: Thu, 19 Apr 2001 11:44:31 -0500 From: Vipin Malik MIME-Version: 1.0 To: joakim.tjernlund@lumentis.se CC: mtd@infradead.org, Nicolas Pitre , David Woodhouse Subject: Re: JFFS2 as root FS References: <000801c0c8bb$44e56de0$0a01a8c0@Win1> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-mtd@infradead.org List-ID: > Now I am having some other problems :-( > First it takes about 1 min 30 sec to mount my root FS. Is that expected? I > was hoping for a much shorter > mount time, 10-20 sec > The root partition is 15 MB and df reports: > > Filesystem 1k-blocks Used Available Use% Mounted on > /dev/mtdblock1 15104 6580 8524 44% /mnt/mtdblock1 Just for reference, my AMD SC520 -100MHz (a 100MHz 486+) with a 8MB, 57% full JFFS2 f/s takes ~19 seconds to mount. The flash is connected on a 32bit bus. Even if it takes 700us (for max wait states on my system) per quad word read (32bits), the entire flash can be read in 1.46 seconds. Even if your flash is connected x8 wide, your flash read times should not be more than 10-12seconds. Obviously, as my flash read time is only ~2 seconds of my 19s fs mount time, the processor speed plays quite a significant role in the mount process. To test this theory, I upped the speed to 133MHz and then it took ~15seconds to mount. The increase in clock speed was 33%, the mount was (19-15)/15 = 26% faster. However, if I remove the "constant" portion of the two mounts- the flash read which is not any faster, then the increase in mount speed = ((19-1.46) - (15-1.46))/ (15 - 1.46) = 29.5% faster, almost linear with the increase with clock speed! (This also tells me that the code is executing primarily out of cache). If you say, that your system takes ~90seconds to mount. Let's say that your flash read time is ~10 seconds (for 16MB), then if all else is ok, your processor should be ~80/17.5 = 4.5 times slower than mine. This assumes equal amount of processing. But your processor is doing about (6580/4636 = 140%) more processing than mine. Assuming linear overhead, then the new factor is ~57/18 = 3.1X slower. (your flash usage is 6580 blocks, mine is 4636 blocks). Now you say that you are using a MPC869T. I did not find a 869T on the web. I presume that you meant 860T. At what MHz? The 860T is claimed to have a performance of ~66 Dhrystone MIPS at 50MHz. I downloaded Dhrystone 2.1 and that give me 51 mips at 100Mhz (and 67.7at 133MHz). However, my 486 has a 16KB combined cache and a 66MHz SDRAM bus. The FLASH is not cached, so the entire cache can be used for the instruction execution. The 860T has only 4KB of instruction cache. Under some circumstances (when the code fits in the cache in my processor and not in yours), the SC520 will behave like a 100MHz machine while the PPC will be limited to the bus clock speed. What is you bus clock speed (and your core clock speed). If your BUS clock is ~25-33 MHz, it's not unbelievable that your processor runs ~2-3X slower, specially if your processor core is running at <50MHz. Also remember that execution from cache is significantly faster than execution from EDO DRAM on the bus. Something to think about. Of course it could be something completely different, like a bug in David's code ;) Vipin To unsubscribe, send "unsubscribe mtd" to majordomo@infradead.org