X-Git-Url: https://git.proxmox.com/?a=blobdiff_plain;f=hw%2F9pfs%2Fcoth.h;h=c51289903d0df0ff65f9d3f2649bbe78b490fee9;hb=da9f2eda2551c1cbd98f72730e5b754f2149a85c;hp=fd4a45bc7c35997c048fde284f527ebd68629c57;hpb=d2c5cf7ca15490b4737a5393e51abf0301b98971;p=mirror_qemu.git

diff --git a/hw/9pfs/coth.h b/hw/9pfs/coth.h
index fd4a45bc7c..c51289903d 100644
--- a/hw/9pfs/coth.h
+++ b/hw/9pfs/coth.h
@@ -19,7 +19,7 @@
 #include "qemu/coroutine.h"
 #include "9p.h"
 
-/*
+/**
  * we want to use bottom half because we want to make sure the below
  * sequence of events.
  *
@@ -28,6 +28,16 @@
  *   3. Enter the coroutine in the worker thread.
  * we cannot swap step 1 and 2, because that would imply worker thread
  * can enter coroutine while step1 is still running
+ *
+ * @b PERFORMANCE @b CONSIDERATIONS: As a rule of thumb, keep in mind
+ * that hopping between threads adds @b latency! So when handling a
+ * 9pfs request, avoid calling v9fs_co_run_in_worker() too often, because
+ * this might otherwise sum up to a significant, huge overall latency for
+ * providing the response for just a single request. For that reason it
+ * is highly recommended to fetch all data from fs driver with a single
+ * fs driver request on a background I/O thread (bottom half) in one rush
+ * first and then eventually assembling the final response from that data
+ * on main I/O thread (top half).
  */
 #define v9fs_co_run_in_worker(code_block)                               \
     do {                                                                \