db6711b7a1
In power7_marked_instr_event() there is a switch case that is missing a break or an explicit fallthrough, it's not immediately clear which it should be. The function determines based on the PMU event code, whether the event is a "marked" event (which then requires us to configure the PMU in a certain way). On Power7 there is no specific bit(s) in the event to tell us that, we just have to know. Rather than having a full list of every event and whether they are marked, we pull apart the event code and for events with certain values of certain fields we can say that those are all marked events. We take the psel (bits 0-7) of the event, and look at bits 4-7. For a value of 6 we say that if the entire psel == 0x64 then if the pmc == 3 the event is marked, else not, and otherwise we continue. It is then that we fallthrough to the 8 case, where we return true if the unit == 0xd. The question is should the 6 case also fallthrough and check for unit == 0xd, or should it return. Looking at the full list of events we see that there are zero events where (psel >> 4) == 0x6 and unit == 0xd. So the answer is it doesn't really matter, there are no valid event codes that will return a different result whether we fallthrough or break. But equally, testing the 6 case events against unit == 0xd is slightly bogus, as there are no such events. So to make the code clearer, and avoid any future confusion, have the 6 case break rather than falling through. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com> |
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README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.