On Thu, Oct 18, 2018 at 1:52 PM Joe Orton <[email protected]> wrote:
>
> On Thu, Oct 18, 2018 at 12:51:06PM +0200, Ruediger Pluem wrote:
> > >>>
> > >>> Curiously inefficient writev use when stracing the process, though,
> > >>> dunno what's going on there (trunk/prefork):
> > >>>
> > >>> writev(46, [{iov_base="\r\n", iov_len=2}], 1) = 2
> > >>> writev(46, [{iov_base="1f84\r\n", iov_len=6}], 1) = 6
> > >>> writev(46, [{iov_base="<D:lockdiscovery/>\n<D:getcontent"...,
> > >>> iov_len=7820}], 1) = 7820
> > >>> writev(46, [{iov_base="<D:supportedlock>\n<D:lockentry>\n"...,
> > >>> iov_len=248}], 1) = 248
> > >>
> > >> The reason is ap_request_core_filter. It iterates over the brigade and
> > >> hands over each bucket alone to
> > >> ap_core_output_filter. IMHO a bug.
> > >
> > > How about the attached patch for fixing?
> >
> > Scratch that. I guess it is much more complex.
>
> Hmm, well it works for me and looks correct, it batches up those the
> writev(,,1) calls as expected, but it seems YMMV :)
After a closer look into this, Rüdiger's patch seems indeed incomplete.
What we possibly want is keep buckets in tmp_bb until it's time to
pass it down the chain, per ap_filter_reinstate_brigade() logic (i.e.
FLUSH bucket, size limit, ...).
I tried to implement that in the attached patch, WDYT?
>
> I notice the function is doing unconditional blocking reads without
> flushing first - rule 10 of the golden rules of output filters! --
The patch also addresses this.
Regards,
Yann.
Index: server/request.c
===================================================================
--- server/request.c (revision 1843207)
+++ server/request.c (working copy)
@@ -2066,8 +2066,10 @@ AP_CORE_DECLARE_NONSTD(apr_status_t) ap_sub_req_ou
AP_CORE_DECLARE_NONSTD(apr_status_t) ap_request_core_filter(ap_filter_t *f,
apr_bucket_brigade *bb)
{
+ apr_status_t status = APR_SUCCESS;
+ apr_read_type_e block = APR_NONBLOCK_READ;
+ conn_rec *c = f->r->connection;
apr_bucket *flush_upto = NULL;
- apr_status_t status = APR_SUCCESS;
apr_bucket_brigade *tmp_bb;
int seen_eor = 0;
@@ -2092,6 +2094,7 @@ AP_CORE_DECLARE_NONSTD(apr_status_t) ap_request_co
/* Don't touch *bb after seen_eor */
while (status == APR_SUCCESS && !seen_eor && !APR_BRIGADE_EMPTY(bb)) {
apr_bucket *bucket = APR_BRIGADE_FIRST(bb);
+ apr_bucket *pass_upto = NULL;
if (AP_BUCKET_IS_EOR(bucket)) {
/* pass out everything and never come back again,
@@ -2098,6 +2101,7 @@ AP_CORE_DECLARE_NONSTD(apr_status_t) ap_request_co
* r is destroyed with this bucket!
*/
APR_BRIGADE_CONCAT(tmp_bb, bb);
+ pass_upto = APR_BRIGADE_LAST(tmp_bb);
ap_remove_output_filter(f);
seen_eor = 1;
}
@@ -2116,31 +2120,61 @@ AP_CORE_DECLARE_NONSTD(apr_status_t) ap_request_co
* something safe to pass down to the connection filters without
* needing to be set aside.
*/
- if (!APR_BUCKET_IS_METADATA(bucket)
- && bucket->length == (apr_size_t)-1) {
+ if (bucket->length == (apr_size_t)-1) {
const char *data;
apr_size_t size;
- status = apr_bucket_read(bucket, &data, &size, APR_BLOCK_READ);
+
+ status = apr_bucket_read(bucket, &data, &size, block);
if (status != APR_SUCCESS) {
- break;
+ if (!APR_STATUS_IS_EAGAIN(status)
+ || block != APR_NONBLOCK_READ) {
+ break;
+ }
+ /* Flush everything so far and retry in blocking mode */
+ pass_upto = apr_bucket_flush_create(c->bucket_alloc);
+ APR_BRIGADE_INSERT_TAIL(tmp_bb, pass_upto);
+ block = APR_BLOCK_READ;
}
+ else {
+ block = APR_NONBLOCK_READ;
+ }
}
- /* pass each bucket down the chain */
- APR_BUCKET_REMOVE(bucket);
- APR_BRIGADE_INSERT_TAIL(tmp_bb, bucket);
+ /* Move the bucket (if any) to tmp_bb and check whether it exhausts
+ * bb or brings tmp_bb above the limit; in both cases it's time to
+ * pass things down the chain.
+ */
+ if (!pass_upto) {
+ APR_BUCKET_REMOVE(bucket);
+ APR_BRIGADE_INSERT_TAIL(tmp_bb, bucket);
+ if (!APR_BRIGADE_EMPTY(bb)) {
+ ap_filter_reinstate_brigade(f, tmp_bb, &pass_upto);
+ }
+ else {
+ pass_upto = bucket;
+ }
+ }
}
- status = ap_pass_brigade(f->next, tmp_bb);
- apr_brigade_cleanup(tmp_bb);
+ /* Pass tmp_bb when asked above only */
+ if (pass_upto) {
+ status = ap_pass_brigade(f->next, tmp_bb);
+ apr_brigade_cleanup(tmp_bb);
+ }
}
+ /* Don't touch *bb after seen_eor */
+ if (!seen_eor) {
+ apr_status_t rv;
+ APR_BRIGADE_PREPEND(bb, tmp_bb);
+ rv = ap_filter_setaside_brigade(f, bb);
+ if (status == APR_SUCCESS) {
+ status = rv;
+ }
+ }
+
ap_release_brigade(f->c, tmp_bb);
- /* Don't touch *bb after seen_eor */
- if (status == APR_SUCCESS && !seen_eor) {
- status = ap_filter_setaside_brigade(f, bb);
- }
return status;
}
