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authorJustus Winter <4winter@informatik.uni-hamburg.de>2014-04-17 15:44:12 +0200
committerJustus Winter <4winter@informatik.uni-hamburg.de>2014-11-03 13:46:29 +0100
commit9480792609c779516ac465ac5a038101032be77d (patch)
tree4be080b62123227c4e6f1bf7ee400af3455e8801 /storeio/pager.c
parent282e4ae275dc1b9b0b5bba6eb1b145cd1e80fa33 (diff)
libpager: use a fixed number of threads
Previously, libpager used an unbounded number of threads to receive messages from the pager bucket. It used sequence barriers to execute the requests to order requests to each object. The sequence barriers are implemented in seqnos.c. A server function uses _pager_wait_for_seqno to wait for its sequence number and _pager_release_seqno to release it, or it uses _pager_update_seqno to do both operations in one step. These sequence barriers divide each server function in three parts: A, B, and C. A_i happens "before" the sequence barrier i, B_i happens "in order", C_i happens "after" the sequence barrier. This partial order < has the following properties: * This order is *per object*. Requests to different objects are not ordered. * A_i < B_i, B_i < C_i (due to the structure of the code) * B_i < B_{i+1} (this is due to the sequence barriers) * Note that only the B parts are ordered by the sequence numbers, we are free to execute C_i and C_{i+1} in any possible order. The same argument applies to the A parts. The sequence barriers are implemented using a very simple ticket algorithm. Every request, even the invalid ones, is processed by a thread, and waits until the ticket count reaches its seqno, does some work in-order, then increments the ticket and awakes all threads that have piled up up to this moment. All of them except one will then discover that it's not their turn yet and go to sleep again. Creating one thread per request has proven to be problematic as memory_object requests often arrive in large batches. This patch does two things: * Use a single thread to receive messages from the port bucket. All incoming request are put into a queue. * Use a fixed-number of threads (though even one is actually enough) to execute the the server functions. If multiple threads are used, a work-delegation mechanism ensures that the per object order < is preserved. For reference, I used the following command to create workloads that highlight the problem this patch is addressing: % settrans t .../ext2fs --sync=30 /dev/sd2s1 ... % /usr/bin/time zsh -c 'for ((i=0; i < 1500; i++)); do dd if=/dev/zero of=t/src/$i bs=4k count=290 2>/dev/null echo -n . if ((i % 100 == 0)) ; then echo -n $i; fi done' * libpager/queue.h: New file. * libpager/demuxer.c: Manage a queue of requests received from the port bucket. (pager_demuxer): Just decode the server function and enqueue the request. (worker_func): New function that consumes and executes the requests from the queue. (service_paging_requests): New function. (pager_start_workers): Likewise. * libpager/data-request.c: Remove the seqno barriers. * libpager/data-return.c: Likewise. * libpager/data-unlock.c: Likewise. * libpager/chg-compl.c: Likewise. * libpager/lock-completed.c: Likewise. * libpager/no-senders.c: Likewise. * libpager/notify-stubs.c: Likewise. * libpager/object-init.c: Likewise. * libpager/object-terminate.c: Likewise. * libpager/seqnos.c: Remove file. * libpager/stubs.c: Likewise. * libpager/pager.h (pager_demuxer): Drop declaration. (pager_start_workers): New declaration. * libpager/priv.h: Remove the _pager_seqno declarations. * libpager/Makefile (SRCS): Drop seqnos.c. * console/pager.c (user_pager_init): Call pager_start_workers. * libdiskfs/disk-pager.c: Likewise. * storeio/pager.c: Likewise. * ext2fs/pager.c (service_paging_requests): Remove function. (create_disk_pager): Start separate file pager using `pager_start_workers'. * fatfs/pager.c (service_paging_requests): Remove function. (create_fat_pager): Start separate file pager using `pager_start_workers'.
Diffstat (limited to 'storeio/pager.c')
-rw-r--r--storeio/pager.c26
1 files changed, 5 insertions, 21 deletions
diff --git a/storeio/pager.c b/storeio/pager.c
index 7d787110..c260d732 100644
--- a/storeio/pager.c
+++ b/storeio/pager.c
@@ -24,6 +24,7 @@
#include <strings.h>
#include <unistd.h>
#include <errno.h>
+#include <error.h>
#include <sys/mman.h>
#include <stdio.h>
@@ -142,21 +143,6 @@ pager_clear_user_data (struct user_pager_info *upi)
static struct port_bucket *pager_port_bucket = 0;
-/* A top-level function for the paging thread that just services paging
- requests. */
-static void *
-service_paging_requests (void *arg)
-{
- (void) arg;
-
- for (;;)
- ports_manage_port_operations_multithread (pager_port_bucket,
- pager_demuxer,
- 1000 * 30, 1000 * 60 * 5, 0);
-
- return NULL;
-}
-
/* Initialize paging for this device. */
static void
init_dev_paging ()
@@ -173,14 +159,12 @@ init_dev_paging ()
pager_port_bucket = ports_create_bucket ();
- /* Make a thread to service paging requests. */
- err = pthread_create (&thread, NULL, service_paging_requests, NULL);
- if (!err)
- pthread_detach (thread);
- else
+ /* Start libpagers worker threads. */
+ err = pager_start_workers (pager_port_bucket);
+ if (err)
{
errno = err;
- perror ("pthread_create");
+ error (0, err, "pager_start_workers");
}
}
pthread_mutex_unlock (&pager_global_lock);