On Tue, Jun 04, 2024 at 12:15:51PM -0400, Steven Rostedt wrote: > On Tue, 04 Jun 2024 12:13:15 +0200 > Paolo Abeni <pabeni@xxxxxxxxxx> wrote: > > > On Thu, 2024-05-30 at 20:16 +0000, Mina Almasry wrote: > > > diff --git a/net/core/devmem.c b/net/core/devmem.c > > > index d82f92d7cf9ce..d5fac8edf621d 100644 > > > --- a/net/core/devmem.c > > > +++ b/net/core/devmem.c > > > @@ -32,6 +32,14 @@ static void net_devmem_dmabuf_free_chunk_owner(struct gen_pool *genpool, > > > kfree(owner); > > > } > > > > > > +static inline dma_addr_t net_devmem_get_dma_addr(const struct net_iov *niov) > > > > Minor nit: please no 'inline' keyword in c files. > > I'm curious. Is this a networking rule? I use 'inline' in my C code all the > time. It mostly comes from Documentation/process/coding-style.rst: 15) The inline disease ---------------------- There appears to be a common misperception that gcc has a magic "make me faster" speedup option called ``inline``. While the use of inlines can be appropriate (for example as a means of replacing macros, see Chapter 12), it very often is not. Abundant use of the inline keyword leads to a much bigger kernel, which in turn slows the system as a whole down, due to a bigger icache footprint for the CPU and simply because there is less memory available for the pagecache. Just think about it; a pagecache miss causes a disk seek, which easily takes 5 milliseconds. There are a LOT of cpu cycles that can go into these 5 milliseconds. A reasonable rule of thumb is to not put inline at functions that have more than 3 lines of code in them. An exception to this rule are the cases where a parameter is known to be a compiletime constant, and as a result of this constantness you *know* the compiler will be able to optimize most of your function away at compile time. For a good example of this later case, see the kmalloc() inline function. Often people argue that adding inline to functions that are static and used only once is always a win since there is no space tradeoff. While this is technically correct, gcc is capable of inlining these automatically without help, and the maintenance issue of removing the inline when a second user appears outweighs the potential value of the hint that tells gcc to do something it would have done anyway. Jason
