Hello everybody, I've been following this thread with much attention and interest, and I would like to give my small contribution, even though my expertise is far lower than yours. Our TX49 (R4000 based) manual also states that "if the CACHE instruction is issued for the line in which this instruction exists the operation is not guaranted". As you can see from the arch/mips/mm/r4xx0.c file, TX49 routines always disable caches before operating. Recently, one of our customer, raised the question since he was comparing performance between TX49 and another comparable MIPS architecture. He noticed a huge difference in favor of the other vendor. For information it was a multimedia application. Investigations showed that the other vendor was running cache flushing operations cached. He tried to also run TX49 cached and, miracle, TX49 performed much better than the other chip. And the application could run for hours without crashing. I have contacted our designers, and the answer I got so far is that a problem can occur depending on the alignement of the CACHE instructions and on the set in which they are located (TX49 cache is 4 way set). This confirms Jon's investigation. Carsten, can you comment this, as a MIPS insider ? Which CPUs are concerned ? Further investigation are now ongoing to find a proper workaround and thus suggestions are highly apreciated. >From my side I have a very simple question: If you run instruction cache flushing cached, then the cache will be dirty when the routine returns. At least the line(s) containing the routine itself ? Or am I missing something ? Best Regards, Mohamed SEDJAI TOSHIBA Electronics Europe PS: Sorry Dominic for a possible misusage of the terminology. BTW I found your book wonderfully well written and consider it as a reference to anyone who wants to write a technical book. -----Original Message----- From: Jon Burgess [mailto:Jon_Burgess@eur.3com.com] Sent: Donnerstag, 11. Juli 2002 18:34 To: Ralf Baechle Cc: Gleb O. Raiko; linux-mips@oss.sgi.com; carstenl@mips.com Subject: Re: mips32_flush_cache routine corrupts CP0_STATUS with gcc-2.96 > Ralf wrote: >Have you tried to insert a large number of nops instead? My investigation suggests that a single extra nop is sufficient. I have also tried inserting extra nops before the cache routine to see if the relative alignment of the instructions with respect to the cacheline has an influence, but it has no effect. I am suspicious that if this occurs with the instruction following the loop then something odd might be occuring on every loop iteration as well. I might try adjusting the instructions in the loop to see if that has any effect. > Or preferably, >how about replacing the __restore_flags() in your example with the >following piece of inline assembler: > > __asm__ __volatile__("mtc0\t%0, $12" ::"r" (flags) : "memory"); I am happy that the current assembler code looks correct, but this change would make it simpler. Jon
