> > The PROD/CONS_ALIGN values on x86-64 are set to 2 cache lines, so members of > struct rte_ring are 128 byte aligned, >and therefore the whole struct needs 128-byte alignment according to the ABI >so that the 128-byte alignment of the fields can be guaranteed.
Ah ok, missed the fact that rte_ring is 128B aligned these days. BTW, I probably missed the initial discussion, but what was the reason for that? Konstantin > > If the allocation is only 64-byte aligned, the beginning of the prod and cons > fields may not actually be 128-byte aligned (but we've told the > compiler that they are using the __rte_aligned macro). Accessing these > fields when they are misaligned will work in practice on x86 (as long > as the compiler doesn't use e.g. aligned SSE instructions), but it is > undefined behavior according to the C standard, and UBSan (- > fsanitize=undefined) checks for this. > > Thanks, > -- Daniel Verkamp > > > -----Original Message----- > > From: Ananyev, Konstantin > > Sent: Friday, June 2, 2017 1:52 PM > > To: Verkamp, Daniel <daniel.verk...@intel.com>; dev@dpdk.org > > Cc: Verkamp, Daniel <daniel.verk...@intel.com> > > Subject: RE: [dpdk-dev] [PATCH v2] ring: use aligned memzone allocation > > > > > > > > > -----Original Message----- > > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Daniel Verkamp > > > Sent: Friday, June 2, 2017 9:12 PM > > > To: dev@dpdk.org > > > Cc: Verkamp, Daniel <daniel.verk...@intel.com> > > > Subject: [dpdk-dev] [PATCH v2] ring: use aligned memzone allocation > > > > > > rte_memzone_reserve() provides cache line alignment, but > > > struct rte_ring may require more than cache line alignment: on x86-64, > > > it needs 128-byte alignment due to PROD_ALIGN and CONS_ALIGN, which are > > > 128 bytes, but cache line size is 64 bytes. > > > > Hmm but what for? > > I understand we need our rte_ring cche-line aligned, > > but why do you want it 2 cache-line aligned? > > Konstantin > > > > > > > > Fixes runtime warnings with UBSan enabled. > > > > > > Fixes: d9f0d3a1ffd4 ("ring: remove split cacheline build setting") > > > > > > Signed-off-by: Daniel Verkamp <daniel.verk...@intel.com> > > > --- > > > > > > v2: fixed checkpatch warnings > > > > > > lib/librte_ring/rte_ring.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/lib/librte_ring/rte_ring.c b/lib/librte_ring/rte_ring.c > > > index 5f98c33..6f58faf 100644 > > > --- a/lib/librte_ring/rte_ring.c > > > +++ b/lib/librte_ring/rte_ring.c > > > @@ -189,7 +189,8 @@ rte_ring_create(const char *name, unsigned count, int > > socket_id, > > > /* reserve a memory zone for this ring. If we can't get rte_config or > > > * we are secondary process, the memzone_reserve function will set > > > * rte_errno for us appropriately - hence no check in this this > > > function */ > > > - mz = rte_memzone_reserve(mz_name, ring_size, socket_id, mz_flags); > > > + mz = rte_memzone_reserve_aligned(mz_name, ring_size, socket_id, > > > + mz_flags, __alignof__(*r)); > > > if (mz != NULL) { > > > r = mz->addr; > > > /* no need to check return value here, we already checked the > > > -- > > > 2.9.4
