event/octeontx2: add devargs to control timer adapters

[dpdk.git] / doc / guides / prog_guide / env_abstraction_layer.rst

diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
index c134636..f15bcd9 100644 (file)
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -147,6 +147,14 @@ A default validator callback is provided by EAL, which can be enabled with a
 ``--socket-limit`` command-line option, for a simple way to limit maximum amount
 of memory that can be used by DPDK application.
 
+.. warning::
+    Memory subsystem uses DPDK IPC internally, so memory allocations/callbacks
+    and IPC must not be mixed: it is not safe to allocate/free memory inside
+    memory-related or IPC callbacks, and it is not safe to use IPC inside
+    memory-related callbacks. See chapter
+    :ref:`Multi-process Support <Multi-process_Support>` for more details about
+    DPDK IPC.
+
 + Legacy memory mode
 
 This mode is enabled by specifying ``--legacy-mem`` command-line switch to the
@@ -214,6 +222,24 @@ Normally, these options do not need to be changed.
     can later be mapped into that preallocated VA space (if dynamic memory mode
     is enabled), and can optionally be mapped into it at startup.
 
++ Segment file descriptors
+
+On Linux, in most cases, EAL will store segment file descriptors in EAL. This
+can become a problem when using smaller page sizes due to underlying limitations
+of ``glibc`` library. For example, Linux API calls such as ``select()`` may not
+work correctly because ``glibc`` does not support more than certain number of
+file descriptors.
+
+There are two possible solutions for this problem. The recommended solution is
+to use ``--single-file-segments`` mode, as that mode will not use a file
+descriptor per each page, and it will keep compatibility with Virtio with
+vhost-user backend. This option is not available when using ``--legacy-mem``
+mode.
+
+Another option is to use bigger page sizes. Since fewer pages are required to
+cover the same memory area, fewer file descriptors will be stored internally
+by EAL.
+
 Support for Externally Allocated Memory
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -563,6 +589,16 @@ Known Issues
 
   5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR.
 
+  Alternatively, applications can use the lock-free stack mempool handler. When
+  considering this handler, note that:
+
+  - It is currently limited to the x86_64 platform, because it uses an
+    instruction (16-byte compare-and-swap) that is not yet available on other
+    platforms.
+  - It has worse average-case performance than the non-preemptive rte_ring, but
+    software caching (e.g. the mempool cache) can mitigate this by reducing the
+    number of stack accesses.
+
 + rte_timer
 
   Running  ``rte_timer_manage()`` on a non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed.
@@ -705,7 +741,7 @@ The most important fields in the structure and how they are used are described b
 
 Malloc heap is a doubly-linked list, where each element keeps track of its
 previous and next elements. Due to the fact that hugepage memory can come and
-go, neighbouring malloc elements may not necessarily be adjacent in memory.
+go, neighboring malloc elements may not necessarily be adjacent in memory.
 Also, since a malloc element may span multiple pages, its contents may not
 necessarily be IOVA-contiguous either - each malloc element is only guaranteed
 to be virtually contiguous.